Jig

A jig is a custom-made manufacturing device that locates and guides a tool—most commonly a drill, reamer, or tap—to ensure repeatable, accurate feature placement; unlike a fixture, a jig’s defining function is tool guidance, not just part holding.

In CNC machining and secondary operations, jigs are most useful where the process depends on tool-entry control rather than full CNC path control, such as drilling, reaming, tapping, boring, rework, and low-volume jobs where a dedicated fixture is not economical. A drill jig often uses guide bushings or a hardened template plate so the drill enters at the correct angle and center location, reducing operator variation and improving interchangeability of parts. On a CNC cell, true jigs are less common for primary milling because the CNC program already controls tool motion; the workholding role is handled by a fixture, while a jig may still be used for secondary hole-making, setup transfer, or odd-shaped manual operations. In millwork and panel assembly, a jig functions as a repeatability template for hinge cups, shelf-pin rows, dowel patterns, or edge-treatment operations, keeping hole spacing and edge offsets consistent across panels.