Making dimensional measurements is a critical part of everyday operations in fields such as manufacturing, machining, metalworking, woodworking, engineering, drafting, automotive maintenance, medicine, and scientific research. Various measurement tools are available, from basic rulers for linear measurement to ultrasonic thickness gauges for nondestructive testing of material thickness.
A ruler is a tool with an inch, metric, or both inch and metric scale for measuring distances and marking lines. A straight edge is used to draw or scribe straight lines and often does not have graduations. To set and measure angles through either 180 or 360 degrees, a protractor may be used.
A caliper measures the inside and outside dimensions of an object as well as the depth of a hole, displaying measurements on a vernier scale, dial, or digital readout. Most calipers are either pivot-type with two legs that mark the points of measurement, or slide-type with a set of adjustable jaws. A micrometer measures either the external dimensions of an object or internal dimensions such as the diameter of a hole or the width of a groove. It has a screw mechanism for precise adjustment of the measuring faces.
There are a variety of gauges for dimensional measurement. A chamfer gauge measures the largest diameter of a chamfer, or beveled edge, while a countersink gauge measures the largest diameter of a countersunk hole. A bore gauge, or hole gauge, measures the distance between the sides of a hole. Depth gauges measure the depth of a hole, slot, step, or recess. Height gauges are used to determine the height of an object. A radius gauge checks the radius of a groove, corner, or other rounded surface. Pin gauges are cylindrical plugs for measuring the diameter of machined holes and slots. Ring gauges are metal bands for go/no-go inspections and may serve as a master for other measurement tools. A snap gauge is used to make comparative measurements of the outside dimensions of objects. Thread gauges check the thread size and pitch diameter of threaded parts. A feeler gauge measures gaps between parts. Thickness gauges measure the thickness of materials. Many gauges incorporate a dial indicator that displays readings.