Squares are used to indicate, by visual comparison, whether two surfaces are perpendicular.

Protractors and angle gages measure the angle between two surfaces of a part or assembly.

Metric gears are defined by module, which designates the center-to-center distance between successive teeth.

DC servomotors are generally small and powerful for their size, and easy to control.

Gearmotors consist of an AC or DC motor with an integral gearbox or gear head that steps delivered speed up or down.

DC motors are most commonly used in variable speed and torque applications.

AC motors include single, multiphase, universal, induction, synchronous, and gear motors.