Patents.
3,767,285; 3,770,966; 3,792,924; 3,834,808; 3,888,568; 3,920,326; 3,920,330; 3,920,331; 3,922,061; 3,924,924; 3,927,934; 3,928,764; 3,935,382; 3,936,153; 3,938,882; 3,938,884; 3,941,457; 3,944,321; 3,944,322; 3,947,085.