Written by Jody Muelaner
Some common pins used as mechanical fasteners. From left to right: Dowel, slotted, coiled, and split pins.
There are several distinct types of fastener, which may be referred to as a pin. These include small headless nails, sharpened pins used for holding fabrics while sewing, attaching paper to pin boards and the like, and several types of mechanical fasteners.
Pins are an unthreaded mechanical fastener, which are designed to be inserted through preformed holes.
The common types of mechanical fastening pin include:
- Dowel pin: A dowel pin is simply a cylinder of solid material which is inserted through a hole. Typically, the hole has a slight interference fit so that compression of the pin and the resulting friction holds the pin firmly in place. Dowel pins also usually have a chamfered end to enable insertion. Wooden dowels are used in joinery while metal dowels are used for precisely locating mechanical components.
- Slotted pin: This is a pin formed from sheet material rolled into a partial cylinder with a chamfer at each end. The chamfer allows the pin to be forced into a hole which is smaller than the pin’s relaxed diameter. The gap in the cylinder allows the pin to compress to fit into the hole. The sprung nature of the pin then holds it securely in the hole.
- Coiled or spiral roll pin: This is similar to a slotted pin but the sheet material is coiled by more than a complete revolution. A coiled pin is therefore more heavy duty than a slotted pin
- Spring or roll pin: This is a general term for both slotted pins and coiled pins.
- Grooved pin: A grooved pin is a solid pin, typically steel, with three grooves swaged along its length, or a part of its length. This creates a pin with more elasticity than a solid dowel pin but stronger than a spring pin. It is also driven into a tight hole.
- Split pin: A pin which is bent in half so that both ends may be inserted through the same hole. Typically manufactured from a half-circular profile so that the two ends together form a circle which fits into the hole. The bent end is formed into an enlarged end and the double end can be bent outwards to prevent the pin being removed.
- Cotter: A wedge or tapered pin, which is driven into a hole. The tapered nature means that it is compressed as it is driven into the hole, causing friction which prevents it from working loose. The term ‘cotter pin’ is also sometimes used to refer to a split pin, R-clip or circle cotter, especially in the United States.
Filed Under: Fastener pins