Today in 1969, US Patent 3467132 A was issued, an invention of Michael J. Parisi, for his “Beer Keg Fitting with Limit Stops.” There’s no Abstract, although in the description it includes this summary:

A beer keg valve having a body portion which inserts into an opening in the keg and a valve at the inner end of the body limited to 90 rotation by abutments on the valve stem which strike against complementary abutments integral with the inside surface of the valve body.