A pin is a machine element that secures the position of two or more parts of a machine relative to each other. The most commonly used are solid cylindrical pins, solid tapered pins, groove pins, clevis pins, slotted spring pins and spirally coiled spring pins. According to pins function, pins can be made of metals (e.g. steel, stainless steel, copper, or brass), wood, or plastic.

Pins can be used in various applications, such as furniture assembly, automotive manufacturing, and construction. They are particularly useful in situations where precision alignment is important, since they provide an accurate and strong joint without the need for additional hardware like screws or bolts.