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ASME B107.24-2002 — Locking Pliers
🔧 ASME B107.24-2002 is the American National Standard dedicated to locking pliers — commonly called “vise grips” or self-locking pliers. These tools use a toggle or cam mechanism to lock the moving handle once the jaws close, holding a preset clamping force without further effort from the operator. That makes them ideal for weld positioning, riveting, temporary fixturing, and long-duration gripping. Some locking pliers also add a cutter behind the jaws, combining clamping with shearing. Developed by the ASME B107 Hand Tools and Accessories Committee and approved by ANSI on November 8, 2002, the Standard defines the dimensions, functional characteristics, safety considerations, and test methods for these tools.
💡 The core value of locking pliers is “hands-free clamping”: once locked, the jaws hold a constant gripping force even if the operator lets go, significantly boosting productivity at welding and assembly stations.
1. Scope and Classification 📌
This Standard covers the dimensions and functional characteristics of locking pliers suitable for gripping and wrenching operations; some locking wrench pliers are provided with cutters. Products are classified as follows:
- Type I — Locking Pliers:
- Class 1: Straight jaws
- Class 2: Curved jaws — Style A (without cutter) and Style B (with cutter)
- Class 3: Long nose — Style A (without cutter) and Style B (with cutter)
- Class 4: Smooth jaws
- Type II: reserved for future use.
The Standard states that the inclusion of dimensional data does not imply that all products described are stock production sizes; consumers should consult manufacturers for lists of stock sizes.
⚠️ Locking pliers are locking-type clamping tools whose jaw force far exceeds that of ordinary hand pliers. Do not use them for rapid repeated clamping like standard pliers, and avoid precision parts or soft workpieces that could be crushed or whose surfaces could be damaged.
2. Construction Design and Release Mechanisms 🔩
The Standard requires locking pliers to be provided with a toggle or cam device with an adjustable mechanism so the jaws can be clamped and locked, and to be releasable by hand anywhere within the capacity of the pliers by any release mechanism similar to Fig. 1. Typical release mechanisms include lever-style unlock triggers on top of the handle, linked release plates between the handles, and “fast-release” constructions operated by spreading the handles. The jaws must grip and lock workpieces across the rated opening range, and test specimens must withstand the applicable test procedures without cracking or breaking.
| Designation | Jaw Features | Typical Applications |
|---|---|---|
| Type I, Class 1 | Straight jaws | Gripping flat plate, flat bar, and structural shapes |
| Type I, Class 2, Style A | Curved jaws, no cutter | Gripping pipes, rods, and curved workpieces |
| Type I, Class 2, Style B | Curved jaws, with cutter | Gripping pipes plus shearing |
| Type I, Class 3, Styles A/B | Long nose, with/without cutter | Gripping in confined spaces and fine positioning |
| Type I, Class 4 | Smooth jaws | Gripping workpieces that must not be marred |
3. Material and Hardness Requirements 🛡️
The Standard specifies material, handle hardness, and jaw requirements:
- Material: must produce pliers conforming to all requirements, with all parts proportioned for adequate strength and durability.
- Handles: through-hardened from 30 to 50 HRC, or case-hardened to a surface hardness of 75 to 86 HR15N with a case depth of at least 0.010 in (0.25 mm). Handles must be shaped for a comfortable grip and free of rough edges and sharp corners.
- Handle clearance: the minimum clearance between the fixed and movable handles must meet the specified value to prevent finger pinching.
- Surface quality: exterior surfaces free of pits, nodules, burrs, and cracks, with rust-preventive treatment; coatings adherent and uniform.
🚨 Locking pliers rely on toggle self-locking, and jaw forces can reach hundreds of newtons. Always seat the workpiece fully into the jaw root before locking; after locking, never strike the handles or force the release with a cheater bar — the mechanism can suddenly fly open and hurl the workpiece.
4. Test Procedures 📊
Section 5 of the Standard specifies the test procedures:
| Test Item | Description | Acceptance Criterion |
|---|---|---|
| Locking/load test (Table 1) | Apply specified load to the locked pliers | No cracking or breaking; lock maintained |
| Jaw grip test (Table 2) | Grip standard specimens and apply tension | Secure grip without slipping |
| Jaw clearance test (Table 3) | Measure minimum jaw clearance at specified positions | Within the specified clearance |
| Release mechanism check | Test unlocking function across the rated range | Reliable one-hand release |
5. Engineering Practice Essentials 🛠️
- 🔍 Selection: choose the Class/Style by workpiece shape and thickness; for long-term hands-free weld positioning prefer long curved-jaw models; choose Style B with cutter where shearing is also needed.
- 🔧 Adjustment: before locking, turn the adjustment screw so the jaws are slightly smaller than the workpiece, then close the handles to the lock position; over-adjustment damages the workpiece, under-adjustment loses grip.
- 📋 Maintenance: periodically inspect jaw teeth, adjustment screw threads, and release-mechanism freedom; clean and lightly lubricate to prevent rust and binding.
- 📊 Procurement: verify marking (manufacturer name or trademark and size) and hardness documentation; sample test locking and grip performance against the Standard.
6. Frequently Asked Questions ❓
❓ Q: What is the essential difference between locking pliers and ordinary pliers?
A: Ordinary pliers need continuous hand force to hold; locking pliers self-lock through a toggle mechanism, keeping a constant clamping force with no effort after locking — ideal for long-duration, hands-free work.
A: Ordinary pliers need continuous hand force to hold; locking pliers self-lock through a toggle mechanism, keeping a constant clamping force with no effort after locking — ideal for long-duration, hands-free work.
❓ Q: Can locking pliers with a cutter shear wire and bolts?
A: Yes, for soft wire and thin bolts within the cutter’s rated capacity. Exceeding the capacity can chip the cutting edge or damage the tool body — use dedicated cutting tools for heavier material.
A: Yes, for soft wire and thin bolts within the cutter’s rated capacity. Exceeding the capacity can chip the cutting edge or damage the tool body — use dedicated cutting tools for heavier material.
🔍 Q: How do I know how far to turn the adjustment screw?
A: As a rule, the handles should close and lock smoothly after clamping while the workpiece is firmly held. The right setting varies with workpiece size; try the tool on similar workpieces first and observe the grip marks.
A: As a rule, the handles should close and lock smoothly after clamping while the workpiece is firmly held. The right setting varies with workpiece size; try the tool on similar workpieces first and observe the grip marks.
❓ Q: Can locking pliers be used for live electrical work?
A: No. Locking pliers are all-metal tools; the Standard includes no insulation requirements. They must never be used on energized circuits.
A: No. Locking pliers are all-metal tools; the Standard includes no insulation requirements. They must never be used on energized circuits.
