A G-clamp’s principal parts consist of a frame, a number of jaws, a threaded screw and a handle.
Frame
The frame of a G-clamp can also be known as the body. This is the main part of the clamp, and its purpose is to endure the pressure that will be placed upon a workpiece during applications, such as chiselling and sawing.
Jaws
The jaws are the part which grip on to a workpiece in order to hold it in place.
One jaw is fixed, while the other has a metal clamping plate which is attached to the screw and is moveable. This jaw can be adjusted to clamp workpieces of various sizes.
Screw
A G-clamp has a threaded screw which controls the movement of the adjustable jaw. A thread ‘form’ is the shape of the helical ridge around a screw, which usually takes an ACME form on a G-clamp. ACME is one of the most popular thread forms, as the wider base of the thread makes it stronger than other types.
This thread form also gives the clamp a more secure grip.
Handle
The handle is connected to the screw and is used to adjust the jaws. When the handle is rotated clockwise the screw is tightened and the jaws will be closed. When the handle is rotated anti-clockwise, the jaws will open.
A G-clamp has a sliding pin handle, which makes it easier to gain extra leverage when tightening the jaws. It is made out of metal and is connected to the screw by a collar.
This type of handle is often referred to as a tommy bar, due to slang that has derived from the First World War when British soldiers were referred to as “Tommies” and a tommy bar was the name given to a spanner used to assemble and disassemble grenade bombs.