Jigs are devices used in the mechanical manufacturing process to securely hold the workpiece in the correct position for processing or inspection, also known as clamps (qiǎ jǔ). Broadly speaking, any device used in the process to quickly, conveniently, and safely install workpieces can be referred to as a jig.

Jigs are typically composed of locating elements (to determine the correct position of the workpiece within the jig), clamping devices, tool guiding elements (to determine the relative position of the tool to the workpiece or guide the tool direction), indexing devices (allowing multiple station processing in a single installation, categorized into rotary indexing and linear indexing devices), connecting elements, and the jig base (the jig's base).