Caliper

A caliper is an instrument with legs that open and close and indicators (marked off like a slide rule and/or digital) showing a measurement. Calipers used in piercing usually have both the main legs used to measure distance, and inverted ones which can be used to measure the inner diameter of circular body jewelry.

Other uses for calipers in piercing include measuring point-to-point distances when marking the skin, and gauging skin movement for surface piercings.