Dimensional gages and instruments provide quantitative measurements of dimensional and form attributes such as wall thickness, depth, height, length, inner diameter (ID), outer diameter (OD), taper and bore. There are many types of dimensional gages and instruments. Gage blocks or master gages are used to calibrate, check, or set variable or fixed limit gages. Gage systems or stations are large, complex units that are typically available in bench top or floor mounted configurations. Go/no-go, functional, and attribute gages are precision tools for comparative gaging based on fixed limits. Indicators and comparators include a precision spindle whose linear movements are amplified and displayed on a dial or digital display. Dimensional gages and instruments include specialized devices that measure thickness, thread size, pitch, serration, and other parameters. Height gages include micrometer, laser micrometer, and micrometer head gages.

There are several gaging technologies for dimensional gages and instruments. Pneumatic gages use air nozzles or inlets to control airflow and pressure. Pneumatic comparators, digital readouts, and analog amplifiers are used to display air gaging dimensional data. Electronic gages use linear variable differential transformers (LVDTs), capacitance, and inductive or other electronic probes to sense the distance or displacement of a contact or stylus. Mechanical gages rely upon the physical movement or displacement of a gaging element such as a spindle, slide, or stem to determine a part’s dimensions. Micrometers, calipers, indicators, plug gages, and ring gages are examples of mechanical gages. Dimensional gages and instruments that use optical, laser, or video-based technology are also available. 

Selecting dimensional gages and instruments requires an analysis of variables such as part or component geometry, production volume, gaging conditions, and dimensional tolerance requirements. Important specifications for dimensional gages and instruments include range and resolution. Optional features include National Institute of Standards and Technology (NIST) traceability, gage calibration, and tool setting capabilities. Vernier graduated scales display dimensions to an intermediate level such as tenths. Automatic devices that provide statistical variation or process control parameters based on dimensional data often include a personal computer (PC) interface and statistical process control (SPC) software. Some dimensional gages and instruments are handheld and portable. Others are benchtop, table-based, or floor-mounted. Test indicators, dial indicators, and micrometer heads are typically machine-mounted.

Dimensional gages and instruments are available with many different types of displays. Analog devices use a pointer or needle mounted in a disc dial. Digital devices present data in numeric or alphanumeric form and often feature data output capabilities that use serial or other formats. Column and bargraph displays provide a way to present dimensional data graphically. Remote displays are used with electronic and optical gages, probes, and gage heads that lack an integral display and are used in production or hazardous environments. Some dimensional gages and instruments display measurements according to the English or imperial system. Others devices display metric amounts.