Plier, Locking

Quick Answer: A locking plier is a plier whose jaws lock onto a workpiece through a toggle linkage, set by an adjusting screw in the end of one handle. Once locked, the locking plier stays clamped without hand pressure and is freed with a release lever.

The Over-Centre Toggle

The lock depends on an over-centre linkage. As the handles close, a short link between them straightens, and just past the straight position it snaps over centre and is held there by the load itself, so the jaws stay clamped with a large force. Turning the adjusting screw moves the end of that link and sets how wide the jaws are when the lock happens, which is how the grip is matched to the work.

Because it holds without effort, the tool behaves like a small portable clamp. It can hold two sheets together while they are drilled or riveted, grip a stripped or rounded nut that a spanner can no longer turn, or act as a temporary handle on a small part. Jaws may be curved, straight or long-nosed, and some have a wire cutter; the pattern and size of this model can be confirmed.

For clamping work against a bench for longer periods, a G-clamp spreads the pressure through a pad and marks the work less.

Care & Handling

• Set the screw so the plier locks with firm hand pressure; too tight a setting crushes tube and thin parts.
• Release with the lever rather than prising the handles apart.
• Protect soft or finished parts with a cloth, since the serrated jaws leave marks.
• Oil the pivots and the adjusting screw occasionally and remove grit.

Applications

• Holding sheet metal or plastic parts together while drilling or riveting
• Removing nuts and bolts whose heads are rounded or damaged
• Clamping small parts during gluing or marking out
• Demonstrating toggle and over-centre linkages in mechanisms lessons

Specifications

Why Choose LabEquip

Engineering workshops, automobile training bays and technology classrooms use a locking plier as a third hand when parts must stay put. LabEquip carries it in the general lab products range; tell us the jaw pattern you need via the contact page.

Frequently Asked Questions

How do I set the grip on a locking plier?

Open the jaws over the work, then turn the adjusting screw until the jaws just touch it. Squeeze the handles; if they will not lock, back the screw off slightly, and if the grip is weak, tighten it slightly.

How does the lock hold without hand pressure?

The handles drive a toggle link that passes just beyond straight, called over centre. The load on the jaws then pushes the link further into its locked position instead of opening it.

Can it remove a rounded bolt?

Often, yes. Set a tight grip on the flats or the round head, lock the plier and turn steadily. It will mark the head, so it is used when the fastener is already damaged or will be replaced.

Can I use it as a clamp?

For small parts and short jobs, yes. For glued joints or long holding, a G-clamp or a bench vice spreads the pressure better and does not dig into the surface.

Why does the plier not release?

The release lever may be stiff or the grip set too tight. Press the lever firmly; if it is dirty, clean and oil it. Do not strike the handles to open them.

Will the jaws crush tubes?

They can. On thin tube or soft material, set the screw so it locks with light pressure and wrap the part in cloth or thin card to spread the load.

Last Updated: September 2026