JP7836079B2 - Anti-slip attachment for screw-type clamps - Google Patents

Description

This invention relates to an attachment for use with a screw-type clamp, and more particularly to an attachment used to reduce effort and enhance safety by holding the clamp in place to prevent displacement when attaching it to a workpiece and when removing it from the workpiece.

Figure 1 schematically shows an example of a screw-type clamp 10 according to prior art (for example, Patent Document 1). As is well known, this clamp comprises a substantially U-shaped clamp body 11 having a hanging hole 18, a rotating jaw 13 rotatably mounted on one leg 12, and a tightening bolt 15 that threads through the other leg 14. The clamp is configured such that the tightening bolt 15 can be moved forward and backward relative to the rotating jaw 13 by rotating a handle (not shown) attached to the rear end of the tightening bolt 15 (the end shown on the right in the figure).

When attaching such a screw-type clamp 10 to a workpiece W, such as a steel plate, for lifting, as shown in Figure 11, the workpiece W is inserted deep into the opening 16 between the legs 12 and 14 by passing it between the tip of the tightening bolt 15 (or the tip pad if a replaceable tip pad is attached to the tip) and the rotating jaw 13. Then, by rotating the handle in the tightening direction, the tightening bolt 15 is moved closer to the rotating jaw 13 (to the left in Figure 11), and the workpiece W is pressed and clamped between the rotating jaw 13 and the tip of the tightening bolt 15, applying a specified tightening force to the workpiece W. In this state, the workpiece W is lifted. After transporting the workpiece W to the designated location, the handle is rotated in the opposite direction to the tightening direction, moving the tightening bolt 15 away from the rotating jaw 13 (to the right in Figure 11), releasing the tightening force on the workpiece W, and the clamp 10 is removed from the workpiece W.

Japanese Patent Publication No. 2013-244538 (Figure 2)

Screw-type clamps, even relatively small and lightweight ones used for lifting relatively light workpieces such as 30-300 kg, have a mass of 1 kg or more, and clamps used for lifting heavy objects of 1 ton or more often have a mass of 10 kg or more. As mentioned above, when attaching the clamp 10 to the workpiece W, it is necessary to operate the handle with one hand to advance the tightening bolt 15 toward the rotating jaw 13. However, until the specified tightening force is applied to the workpiece W, which is pressed and clamped between the rotating jaw 13 and the tip of the tightening bolt 15, the clamp 10 must be supported with the other hand to maintain the positional relationship with the workpiece W as shown in Figure 11. This is a difficult and laborious task, especially when the clamp 10 has a large mass. If the force supporting the clamp 10 at this time is insufficient, the clamp 10 may be attached at an angle to the workpiece W, preventing the specified tightening force from being applied, and creating a risk of the workpiece W falling during lifting or transportation.

Furthermore, when removing the clamp 10 attached to the workpiece W as shown in Figure 11, it is necessary to operate the handle with one hand to retract the tightening bolt 15. However, even after the clamping force on the workpiece W is released, the clamp 10 must be supported with the other hand, which is a difficult and laborious task, especially when the clamp 10 is heavy. If the force supporting the clamp 10 is insufficient at this time, the clamp 10 may tilt and detach when the clamping force on the workpiece W is released, creating a risk of injury to the worker from the falling clamp 10 or damage from impact with the ground.

Furthermore, other uses of this screw-type clamp 10 include attaching it from below to the steel frame (such as H-beams) of a structural frame in the opposite orientation to Figure 11, and suspending a chain block or similar device from the suspension hole 18 (see Figure 10). Alternatively, a horizontal lifeline for working at height can be attached to the suspension hole 18 of a horizontally mounted clamp 10 and used as a tension clamp. However, in these uses, if the force supporting the clamp 10 is insufficient when attaching it to the steel frame, the clamp 10 cannot be properly attached, creating a risk of injury to workers due to the clamp 10 falling, or damage to the worker upon impact with the ground.

Furthermore, especially when used for upward suspension, removing the clamp 10 from the steel frame requires operating the handle with one hand to retract the tightening bolt 15. However, even after the clamping force on the steel frame is released, the clamp 10 must be supported with the other hand, making it a difficult and laborious task, particularly when the clamp 10 is heavy. If the support force for the clamp 10 is insufficient at this time, the clamp 10 may detach the moment the clamping force on the steel frame is released, creating a risk of injury to the worker from the falling clamp 10 or damage from impact with the ground.

Therefore, the problem that this invention aims to solve is to provide a novel anti-slip attachment that reduces the labor involved in attaching and detaching a screw-type clamp to a workpiece, and enhances safety by preventing accidental falls of the workpiece or clamp. In this specification, the term "workpiece" broadly refers to the mating member to which the screw-type clamp is attached, and includes the lifted object such as a steel plate when the screw-type clamp is used as a lifting clamp, and the existing structural frame such as a steel frame when the screw-type clamp is used as a lowering clamp or tensioning clamp.

To solve this problem, the present invention according to claim 1 is a slip prevention attachment for use in a screw-type clamp configured to lift a workpiece by clamping it between a receiving portion provided on one leg of the clamp body and a tightening bolt provided on the other leg so as to be movable, comprising: a first locking member that can be locked to the tip of the tightening bolt; a second locking member that can be locked to the rear end of the tightening bolt in a manner that is substantially immovable relative to the first locking member and rotatable relative to the second locking member ; a connecting member that connects the first locking member and the second locking member; and a magnet provided at the tip of the first locking member or the connecting member, wherein the first locking member has a through hole into which the tip of the tightening bolt is loosely fitted, and the second locking member has a mounting hole with an opening formed therein that can be attached to an incomplete threaded portion having an unthreaded circumferential surface between the male thread and the flange of the tightening bolt.

The present invention according to claim 2 is characterized in that, in the anti-slip attachment for a screw-type clamp described in claim 1, the opening of the mounting hole has an opening width that is slightly smaller than the diameter of the incomplete thread portion of the tightening bolt .

The present invention according to claim 3 is a screw-type clamp slip prevention attachment according to claim 1 or 2, wherein the connecting member consists of a plurality of collars positioned at a predetermined angle apart with respect to the rotation axis of the attachment, and each collar is formed to have a length substantially equal to the axial distance between the position where the first locking member locks on the tightening bolt and the position where the second locking member locks .

The present invention according to claim 4 is characterized in that, in the anti-slip attachment for a screw-type clamp described in claim 3 , the connecting member consists of three collars arranged at 90-degree intervals in a substantially semicircular region centered on the rotation axis of the attachment, and the distance between two of these three collars, which are arranged opposite each other at 180-degree intervals, is set to be slightly larger than the thickness of the other leg of the screw-type clamp .

According to the present invention as described in claim 1, this slip prevention attachment can be detachably attached to the tightening bolt of a screw-type clamp, and therefore to the clamp, via the first and second locking members. When the workpiece to be lifted is inserted between the receiving portion and the tightening bolt with the slip prevention attachment attached to the clamp, the workpiece is attracted to the magnet and fixed to the clamp, preventing the clamp from falling off the workpiece without manual support. Therefore, the worker only needs to tighten the tightening bolt with one hand, reducing labor and improving work efficiency. Even when lowering the workpiece from a predetermined location, the workpiece remains fixed to the clamp by the magnet even when the tightening bolt is loosened and the pressure against the workpiece is released. This prevents the clamp from accidentally falling off the workpiece, thus preventing injury to the worker or damage to the clamp.

Furthermore, this anti-slip attachment is mounted to a screw-type clamp via first and second locking members. When the workpiece is attracted to the magnet (and therefore fixed integrally with the clamp), it does not hinder the rotation of the tightening bolt, and when the tightening bolt is tightened or loosened, it moves together with the workpiece in the same direction. Therefore, even in this mounted state, it does not interfere with the operation or function of the tightening bolt.

Furthermore, since this anti-slip attachment can be mounted to a clamp by locking the first and second locking members, provided on the attachment side, onto the tip and rear end of the tightening bolt, respectively, existing tightening bolts can be used as is, and no special processing such as groove machining is required. Therefore, it does not lead to a reduction in the strength of the tightening bolt due to processing, and can be provided as a low-cost, highly versatile anti-slip attachment.

Furthermore, the first locking member is designed to prevent it from rotating along with the tightening bolt when it is attached to the clamp.

Furthermore, the second locking member, when attached to the clamp, is designed to not rotate along with the tightening bolt when the bolt rotates, but also to move in conjunction with the forward and backward movement of the tightening bolt.

According to the present invention as of claim 2 , when attaching this slip prevention attachment to the clamp, it can be fitted onto the incomplete thread portion of the tightening bolt by pushing it in while widening the opening of the mounting hole formed in the second locking member, and this state can be maintained to prevent it from accidentally falling off.

According to the present invention as of claim 3 , the first and second locking members are connected via a plurality of collars having a predetermined axial length, making it easy to lock the first and second locking members to predetermined locations on the tightening bolt.

According to the present invention as of claim 4 , the clamp is mounted with two opposing collars positioned on both sides of the other leg of the clamp and the other collar positioned towards the tip of the leg. This arrangement makes it easy to mount the attachment to the clamp by utilizing the approximately semicircular area that is free without any collars. Furthermore, when mounted to the clamp, the two opposing collars are in close contact with both sides of the leg with virtually no gap, which substantially prevents the attachment from rotating along with the tightening bolt when the tightening bolt is rotated, or minimizes the amount of rotation. Therefore, the magnetic attraction to the workpiece can be maintained.

This is a perspective view showing an example of a screw-type clamp to which the anti-slip attachment according to the present invention is attached. This is a perspective view showing a slip prevention attachment according to one embodiment of the present invention. These are the front end view (a) and the rear end view (b) of this anti-slip attachment. This is a cross-sectional view of this anti-slip attachment. This is a perspective view showing the anti-slip attachment mounted on the screw-type clamp shown in Figure 1. Figure 3 is a perspective view showing the positional relationship between the anti-slip attachment and the tightening bolt in the installed state. This is a side view showing a tightening bolt individually. This is an explanatory diagram showing the procedure for attaching this anti-slip attachment to a screw-type clamp. This is a cross-sectional view showing a screw-type clamp equipped with this anti-slip attachment being used as a lifting clamp, with the clamp set on the workpiece via magnetic attraction. This is a cross-sectional view showing a screw-type clamp equipped with this anti-slip attachment being used as a suspension clamp, with the clamp set on the workpiece via magnetic attraction. This is a cross-sectional view showing the positional relationship between a screw-type clamp, without an anti-slip attachment, and a workpiece when used as a lifting clamp.

The configuration and operation of an anti-slip attachment according to one embodiment of the present invention will be described in detail below with reference to Figures 1 to 10.

This anti-slip attachment (hereinafter simply referred to as "attachment") 20 is used by being attached to the screw-type clamp 10 shown in Figure 1. As previously described, this clamp 10 comprises a roughly U-shaped clamp body 11 having a hanging hole 18, a rotating jaw 13 rotatably attached to one of its legs 12, and a tightening bolt 15 that screws through the other leg 14. By rotating a handle (not shown) attached to the rear end of the tightening bolt 15 (the end shown on the right in Figure 1), the tightening bolt 15 can be moved forward and backward relative to the rotating jaw 13.

As shown in Figure 7, the fastening bolt 15 has a male thread 15a formed along its predetermined axial length, and its tip is integrally formed or detachably provided as a separate component, with an engaging tooth for biting into the side surface of the workpiece W to increase the holding force. Furthermore, the rear end of the fastening bolt 15 is provided with a rotating operation portion 15e through which a flange portion 15d, larger in diameter than the male thread 15a, and a mounting hole 17 (Figure 6) for attaching a handle (not shown) are formed, via an unthreaded incomplete thread portion 15c. When threading the shaft member having the flange portion 15d to form the male thread 15a, the threading jig interferes with the flange portion 15d, making it impossible to thread up to the flange portion 15d. Therefore, this portion is grooved to a diameter slightly smaller than the root diameter of the male thread 15a, forming an unthreaded, smooth-surfaced incomplete thread portion 15c.

The attachment 20 comprises a front locking plate 21, a rear locking plate 22, a connecting member 23 that coaxially connects these, and a magnet 24. To minimize the weight increase caused by attaching the attachment 20 to the clamp 10, it is preferable that the attachment 20 be made of the lightest possible material. Furthermore, as described later, the rear locking plate 22 is preferably made of a material that has sufficient flexibility to allow the opening 22a to expand when an external force is applied, and resilience to return to its original opening width B when released from the external force. For example, it may be made of a thin metal plate or a synthetic resin plate. Also, from the viewpoint of achieving both weight reduction and strength, it is a suitable embodiment to form each component of the attachment 20 from engineering plastics such as MC nylon.

The tip locking plate 21 has a through hole 21a with a diameter that allows the tip 15b of the tightening bolt 15 to pass through. The tip locking plate 21 has arm portions 21b, 21c, and 21d that extend outward at 90-degree intervals concentrically with the through hole 21a, and magnets 24a, 24b, and 24c are attached to the tips of each arm portion. It is preferable to use magnets 24a, 24b, and 24c that have strong magnetic force; for example, neodymium magnets are a suitable example. Of these magnets, magnets 24a and 24b are positioned opposite each other at 180 degrees across the through hole 21a, and magnet 24c is positioned at a 90-degree interval to one side of magnets 24a and 24b.

The rear end locking plate 22 has an external shape substantially similar to that of the front end locking plate 21 and has a mounting hole 22a that can be attached to the incomplete threaded portion 15c of the tightening bolt 15. The mounting hole 22a of the rear end locking plate 22 is a circular hole with a diameter slightly larger than the diameter R of the incomplete threaded portion 15c of the tightening bolt 15. However, it is missing over a region slightly smaller than half its circumference, forming an opening 22b with an opening width B slightly smaller than the diameter R of the incomplete threaded portion 15c. The opening 22b is formed in a region where the three collars 23a, 23b, and 23c (described later), which are arranged at 90-degree intervals, are not present; in other words, it is formed in the region opposite to the collar 23c, with the through hole 21a and the fixing hole 22a in between.

In this embodiment, the connecting member 23 is formed as three pipe-shaped members or collars 23a, 23b, 23c that connect the ends of the arm portions 21b, 21c, 21d of the front locking plate 21 and the similar arm portions 22c, 22d, 22e of the rear locking plate 22. The collars 23a, 23b, 23c are formed to be approximately the same length as the length L (Figure 7) of the male thread portion 15a of the tightening screw 15. Furthermore, the lengths of the arm portions of the front locking plate 21 and the rear locking plate 22 are set such that the distance P between collars 23a and 23b, which are positioned opposite each other with respect to the axis of rotation (the axis passing through the center of the through hole 21a and the mounting hole 22a, the same as the axis of rotation of the tightening bolt 15), is slightly larger than the thickness of the leg portion 14 of the clamp 10. Magnets 24a, 24b, and 24c are embedded in or fixed to the respective ends of collars 23a, 23b, and 23c. Screws 25a, 25b, and 25c pass through the magnets 24a, 24b, and 24c, extend rearward through the center of collars 23a, 23b, and 23c, pass through the rear end locking plate 22, and are secured by tightening nuts 26a, 26b, and 26c on the outside.

The procedure for attaching this attachment 20 to the tightening bolt 15 of the clamp 10 will be explained with reference to Figure 8.

First, as shown in Figure 8(a), with the collar 23c of the attachment 20 positioned downwards (farthest from the clamp 10), and the attachment 20 held in a position where the top of the attachment 20 is widely open, the tip 15b of the tightening bolt 15 is inserted into the through hole 21a of the tip locking plate 21, straddling the leg portion 14 of the clamp 10 between the collars 23a and 23b. As previously described, in this embodiment, three collars 23a, 23b, and 23c are provided at 90-degree intervals in a substantially semicircular region centered on the axis of rotation, and the other substantially semicircular region is largely open. Furthermore, the distance P between the opposing collars 23a and 23b, which are spaced 180 degrees apart, is greater than the thickness of the leg portion 14 of the clamp 10. Combined with the fact that the attachment 20 is lightweight overall, this operation can be easily performed.

Next, as shown in Figure 8(b), the rear end locking plate 22 of the attachment 20 is lifted and brought closer to the tightening bolt 15, and the incomplete threaded portion 15c of the tightening bolt 15 is fitted into the opening 22b of the mounting hole 22a. As previously described, the opening width B of the opening 22b is formed to be slightly smaller than the diameter R of the incomplete threaded portion 15c. However, by pushing with strong force, the opening 22b expands through the flexibility of the rear end locking plate 22, and its opening width becomes approximately equal to the diameter R of the incomplete threaded portion 15c. When it is fully fitted into the incomplete threaded portion 15c, the opening 22b returns to its original opening width B through the restorative properties of the rear end locking plate 22. As a result, the attachment 20 is mounted on the tightening bolt 15, and this mounted state is maintained.

Figure 9 shows the state in which the workpiece W is set in the clamp 10 with the attachment 20 attached. As is well known, the tightening bolt 15 is retracted to create a gap between it and the rotating jaw 13 that is sufficiently larger than the thickness of the workpiece W, and the workpiece W is inserted to the deepest part of the opening 16. In the conventional technique without the attachment, as described above with reference to Figure 11, the clamp 10 had to be held by hand to maintain this position. However, by using the clamp 10 with the attachment 20 attached, the workpiece W is attracted to the attachment 10 by the magnetic force of the magnets 24a, 24b, and 24c provided at the tip of the attachment 20, so the clamp 10 can maintain the position shown in Figure 11 without being held by hand.

Therefore, the worker only needs to operate the handle with one hand to move the tightening bolt 15 in the tightening direction, and even when tightening in an unstable position, the correct positional relationship with the workpiece W can be ensured (displacement is prevented), thus greatly reducing the labor required and significantly improving work efficiency. The attachment 20 is attached to the tightening bolt 15 by the tip portion 15b of the tightening bolt being loosely fitted into the through hole 21a of the tip locking plate 21 and the incomplete thread portion 15c of the tightening bolt 15 being fitted into the mounting hole 22a of the rear end locking plate 22. Therefore, it is rotatable relative to the tightening bolt 15, and even when the attachment 20 is attached, it does not hinder the rotation of the tightening bolt 15 and the resulting axial movement. On the other hand, the attachment 20's mounting hole 22a of the rear end locking plate 22 is sandwiched between the threads of the male threaded portion 15a and the flange portion 15d, and is fitted onto the incomplete threaded portion 15c of the tightening bolt 15. Therefore, while the attachment 20 remains attached to the side surface of the workpiece W, it moves together with the tightening bolt 15 in the same direction when the bolt moves axially.

As described above, the tightening bolt 15 is moved toward the rotating jaw 13, and after confirming that the specified tightening force is applied to the workpiece W held between them, the workpiece W is lifted and transported to the designated location. Note that when the tightening bolt 15 is tightened from the state shown in Figure 9, the attachment 20 will also attempt to rotate due to the rotation. However, since the distance P between collars 23a and 23b is set to be slightly larger than the thickness of the leg portion 14 of the clamp 10, even if the attachment 20 rotates along with the bolt, the amount of rotation is very small, and the suction to the workpiece W is not impaired.

After lowering the workpiece W at the designated location, remove the attachment 20 from the clamp 10. This process can be performed by essentially reversing the steps taken during attachment installation as described with reference to Figure 8.

In other words, first, the tightening bolt 15 is loosened to reach the state shown in Figure 9. Since the attachment 20 is attracted to the workpiece W by the magnetic force of magnets 24a, 24b, and 24c, even if the tightening force on the workpiece W is lost by loosening the tightening bolt 15, the clamp 10 will not accidentally detach from the workpiece W.

From this state, after removing the clamp 10 from the workpiece W with a force exceeding the magnetic force of magnets 24a, 24b, and 24c, the rear end locking plate 22 of the attachment 20 is pulled away from the tightening bolt 15, removing the rear end locking plate 22 that was fitted onto the incomplete thread portion 15c of the tightening bolt 15. Furthermore, the front end locking plate 21 is removed from the tip portion 15b of the tightening bolt, thereby detaching the attachment 20 from the clamp 10. The removal of the rear end locking plate 22 from the tightening bolt 15 can also be easily performed through the flexibility of the rear end locking plate 22.

In the above explanation, it is assumed that the screw-type clamp 10 with the attachment 20 attached is used as a lifting clamp for the workpiece W. However, as previously described in relation to the prior art, the screw-type clamp can also be used as a lifting or tensioning clamp. In these uses as well, the screw-type clamp 10 with the attachment 20 can be suitably used, similarly reducing the effort required for attachment/detachment to the workpiece W (steel frame) and increasing safety by preventing the clamp or workpiece from falling or detaching. As an example, when the screw-type clamp 10 with the attachment 20 is used as a lifting clamp, as shown in Figure 10, the clamp 10 is set on the lower end of the workpiece W by pushing it upward from below, the opposite of Figure 9, and is then attracted to and fixed to the workpiece W by the magnet 24.

Although the screw-type clamp slip prevention attachment according to the present invention has been described in detail above based on the illustrated embodiment, the present invention is not limited thereto and can be implemented in a wide variety of ways by modifications and changes within the scope of the invention described in the claims.

For example, in the anti-slip attachment according to the illustrated embodiment, three collars are provided at 90-degree intervals in a substantially semicircular region centered on the axis of rotation, with a magnet at the tip of each collar. As previously described, this facilitates the attachment/detachment of the attachment from the clamp and helps maintain the attachment's grip on the workpiece by preventing it from rotating with the tightening bolt. However, the number and arrangement of the collars and magnets are not particularly limited, as long as sufficient gripping force is exerted on the workpiece. Other embodiments may include, for example, an embodiment in which magnets are provided at the tips of three collars arranged at 120-degree intervals in a circular region centered on the axis of rotation, or an embodiment in which magnets are provided at the tips of four collars arranged at 90-degree intervals in a circular region centered on the axis of rotation.

Furthermore, the anti-slip attachment according to the present invention can be applied to any screw-type clamp, regardless of its shape, structure (e.g., pressure nut type), size, or application (e.g., vertical lifting, horizontal lifting, omnidirectional lifting). The shape and size of each part of the anti-slip attachment can be appropriately designed according to the shape and size of the corresponding part or component of the screw-type clamp to which it will be attached.

Furthermore, in the illustrated embodiment of the anti-slip attachment, a locking means is employed that utilizes the incomplete thread portion of the tightening bolt to secure it to the tightening bolt in a manner that is substantially axially immobile and rotatable relative to the bolt. This means the attachment is fitted to the incomplete thread portion through an opening in a mounting hole formed in the rear end base. However, the attachment is not limited to this configuration, and other configurations may be adopted. For example, a configuration can be adopted in which the flange portion of the tightening bolt is formed in two places slightly separated axially, and the rear end base is loosely fitted between them.

10 Screw-type clamp 11 Clamp body 12 Leg portion 13 Rotating jaw (receiving portion)
14 Leg portion 15 Tightening bolt 15a Male thread 15b Tip portion 15c Incomplete thread portion 15d Flange portion 15e Rotation operation portion 16 Opening 17 Handle mounting hole 18 Hanging hole 20 Anti-slip attachment 21 Tip locking plate (first locking member)
21a Through hole 21b, 21c, 21d Arm portion 22 Rear end locking plate (second locking member)
22a Mounting hole 22b Opening 22c, 22d, 22e Arm portion 23 Connecting member 23a, 23b, 23c Collar 24a, 24b, 24c Magnet 25a, 25b, 25c Screw 26a, 26b, 26c Nut

Claims (4)

A slip prevention attachment for a screw-type clamp configured to lift a workpiece by clamping it between a receiving portion provided on one leg of the clamp body and a tightening bolt provided on the other leg so as to be movable, comprising: a first locking member that can be locked to the tip of the tightening bolt; a second locking member that can be locked to the rear end of the tightening bolt in a manner that is substantially axially immovable relative to the rear end of the tightening bolt and rotatable relative to the rear end ; a connecting member that connects the first locking member and the second locking member; and a magnet provided at the tip of the first locking member or the connecting member, wherein the first locking member has a through hole into which the tip of the tightening bolt is loosely fitted, and the second locking member has a mounting hole with an opening formed therein that can be attached to an incomplete threaded portion of the tightening bolt that has an unthreaded circumferential surface between the male thread and the flange of the tightening bolt. The slip prevention attachment according to claim 1, characterized in that the opening of the mounting hole has an opening width slightly smaller than the diameter of the incomplete thread portion of the tightening bolt . The anti-slip attachment according to claim 1 or 2, characterized in that the connecting member consists of a plurality of collars positioned at a predetermined angle apart with respect to the rotation axis of the attachment, and each collar is formed to have a length substantially equal to the axial distance between the position where the first locking member locks with the fastening bolt and the position where the second locking member locks with the fastening bolt. The anti-slip attachment according to claim 3, characterized in that the connecting member consists of three collars arranged at 90-degree intervals in a substantially semicircular region centered on the rotation axis of the attachment, and the distance between two of these three collars, which are arranged opposite each other at 180-degree intervals, is set to be slightly greater than the thickness of the other leg of the screw-type clamp .