Mainly used for rapid manual assembly and disassembly, quick-release pins use a mechanism to provide a locking action. They use a clearance fit in holes formed to nominal diameters and are divided into two major types -- push-pull pins and positive-locking pins.
Push-pull pins are made with a solid or a hollow shank containing a detent assembly in the form of a locking lug, button, or ball which is backed up by a resilient core, plug, or spring.
These pins are made 0.002 to 0.004 in. undersize to fit any standard hole drilled to nominal-diameter dimensions. Pullout loads can be expected to decrease as looseness of fit increases. Hole edges should be deburred or slightly chamfered to ease assembly.
Primary function of these pins is to fasten parts under shear loading. Ideally, the load direction should be at right angles to the shank of the pin. Locking mechanisms are designed to provide secure retention against accidental disassembly. These pins are not recommended for loads in tension.
Positive-locking pins have a locking action that is usually independent of insertion and removal forces. These pins are also primarily suited for shear-load applications, though some tension loading can be tolerated without affecting pin function.
Positive-locking pins are divided into three categories: heavy-duty cotter pins, single-acting pins, and double-acting pins.
Heavy-duty cotter pins use a forged, high-carbon steel body to replace the conventional split-cotter construction. Locking action is provided by a tempered-steel snap ring mounted on the head of the pin.
Single-acting pins have locking action controlled by a plunger-actuated locking mechanism. In the locked position, the locking element projects beyond the surface of the pin shank to provide a positive lock. When the plunger is moved by means of a button or lever assembly at one end of the pin, the locking element retracts. A number of head styles and release mechanisms have been developed for these pins.
Double-acting pins are a modification of single-action types, and have a bidirectional, spring-located plunger. Movement of the plunger in either direction releases the locking balls.