Patents.
3,157,727; 3,160,752; 3,166,623; 3,175,457; 3,262,359; 3,317,265; 3,317,267; 3,318,650; 3,318,653; 3,319,068; 3,320,014; 3,320,015; 3,320,016; 3,320,017; 3,320,018; 3,320,418; 3,320,425; 3,321,264; 3,322,486; 3,324,297; 3,324,299; 3,326,621; 3,326,622.