Today in 1986, US Patent 4571920 A was issued, an invention of Henry P. Roach and Jeffrey W. Gunn, for their “Beer Keg Capping Machine.” Here’s the Abstract:

A keg capping machine primarily for use with beer kegs having protruding neck portions upon which flexible plastic caps are to be fitted. The machine has a capping head attached to the lower end of an inclined cap chute which is attached on its upper end to a cap storing hopper. The capping head has horizontal flanges on its bottom edge which serve as stops and guideways for caps sliding down the chute. The neck of a keg which is carried along a conveyor moves between the guideways and engages the lower portion of a cap forcing it through the capping head. A cap driving rocker within the capping head is employed to force the cap down tightly onto the neck of the keg.