G-Clamp

Quick Answer: A G-clamp is a C-shaped metal frame with a threaded screw through one end that presses a swivel pad towards the fixed jaw. The G-clamp holds work firmly against a bench for sawing, drilling or gluing, and fixes apparatus to the edge of a lab table.

Frame, Screw and Swivel Pad

Turning the handle drives the screw through the threaded boss in the frame, and the swivel pad on its end tilts slightly to sit flat on the workpiece even when the two faces are not quite parallel. Because a screw thread cannot be pushed back by the load, the grip stays put until the screw is turned the other way. Two measurements define any clamp of this type: the maximum opening between pad and jaw, and the throat depth, which is how far in from an edge it can reach. Neither is stated in this product’s title, so both should be confirmed.

In a physics laboratory the clamp is a quick mounting device. A pulley clamped to the end of a bench carries the string in friction and Atwood-type experiments, and a metre rule clamped at one end becomes a cantilever for studying deflection under load or the vibration of a loaded beam. The clamp keeps the fixed end still, which is what the calculation assumes.

In a workshop the same tool holds boards together while glue sets, pins a template onto sheet material for marking out, and holds a piece against the bench for sawing or drilling where a bench vice cannot take the work.

Applications

• Fixing a pulley or a clamp stand base to the edge of a lab bench
• Holding a metre rule as a cantilever for deflection and oscillation experiments
• Clamping glued joints while the adhesive cures in woodwork and model making
• Holding sheet material or small parts to the bench for drilling and sawing

Specifications

Care & Handling

• Put a scrap of wood or card under the pad and jaw on finished surfaces so they are not dented.
• Tighten by hand only; forcing the handle with a bar can bend the frame or strip the thread.
• Wipe glue squeeze-out off the screw before it sets, and oil the thread occasionally.
• Check the swivel pad is still attached; without it the screw end digs into the work.

Why Choose LabEquip

Physics teachers setting up mechanics experiments, woodwork and technology rooms, and technicians who fix apparatus to benches usually keep several G-clamps of different openings. LabEquip stocks this clamp with its general lab products; list the openings you need on the contact page.

Frequently Asked Questions

What size clamp do I need?

Measure the thickest combined work you will clamp, such as a bench top plus a pulley bracket, and choose an opening comfortably larger. If the clamp must reach in from an edge, check the throat depth as well as the opening.

How is a G-clamp different from an F-clamp?

A G-clamp has a fixed C-shaped frame and a long screw, so it is rigid and compact. An F-clamp has a sliding arm on a bar, giving a much wider range of openings that can be set quickly, but it is usually less stiff for its size.

How do I stop the clamp marking the bench or workpiece?

Place small pieces of scrap wood, cork or card between the pad and the surface, and between the fixed jaw and the other face. They spread the pressure and protect polished or painted surfaces.

Can I use the clamp to hold a metre rule for a cantilever experiment?

Yes. Clamp one end of the rule flat on the bench with a packing block, keep the clamped length the same for every reading, and measure the free length from the edge of the block. A loose clamp gives inconsistent deflection readings.

Why does the swivel pad matter?

The pad tilts to sit flat on a surface that is not parallel to the jaw, spreading the force. Without it, the screw end presses on a point, marks the work and can twist the piece out of position as it tightens.

How tight should the clamp be?

Hand-tight is enough for most jobs. Overtightening can crush timber, starve a glued joint by squeezing out all the adhesive, or bend a light frame. Stop when the work cannot move.

Last Updated: September 2026