Abstract: A robot arm has a tool connected thereto through a coupling apparatus including an inner assembly attached to the robot arm and an outer assembly attached to the tool. When the inner assembly has its outer surface mating with an inner surface of the outer assembly, a piston in the inner assembly is pneumatically moved to lock the inner and outer assemblies to each other. The piston movement causes radial movement of balls, which are mounted in a retainer of the inner assembly, away from the piston so that the balls will be retained beneath a cam locking ring of the outer assembly whereby the inner and outer assemblies remain locked when the pneumatic pressure is removed. The outer surface of the outer assembly has a mounting plate for attachment to the tool to be connected to the robot arm.