Today in 1985, US Patent 4538746 A was issued, an invention of James H. Hines, for his “Keg-Tapping Assembly.” Here’s the Abstract:

The invention contemplates improved safety interlock mechanism incorporated in a keg-tapping assembly which is removably attachable to a standard beer keg or the like, via a bayonet-type engagement between lugs on the keg and a slotted flange on the keg-tapping assembly. The keg-tapping assembly is of the variety in which a handle is depressed to gain beverage-dispensing access to the keg and in which the handle is raised to close the keg and to shut off supply of gas pressure to the keg. A guide formed in the keg-tapping assembly locates a vertically displaceable locking leg, having articulated connection to the handle, such that in a downward actuation of the handle, the guided locking leg will be in a position to deny lug displacement into or through one of the slots of the slotted flange, before handle displacement can either begin to open the keg or to admit gas pressure thereto. The result is that unless the handle is sufficiently raised to allow safe removal of the keg-tapping assembly from a keg, the keg-tapping assembly cannot be removed.