Mechanical play in action: A graph of twist angle versus load depicts how play between individual gear wheels on a gearhead (this example is from a Maxon unit) makes the gearhead’s angle of rotation change suddenly when the direction of rotation reverses, in the absence of a load moment. Under a higher load, the gear wheels begin to deform elastically. A schematic of load versus twisting angle depicts the hysteresis typical of pure elastic torsional play.