The Size 8 by Haydon Kerk Motion Solutions is a 21mm stepper motor linear actuator. Size 8, 21000 series linear actuators are available in three designs - captive, non-captive and external linear versions. Available in a variety of resolutions, ranging from 0.0015mm to 0.04mm per step. The size 8 series stepper motor linear actuator delivers force of up to 10 lbs (44N). Typical applications include medical equipment, semiconductor handling, valve control, X-Y tables, hand held instruments, or wherever precise linear motion is required.