Patents.
3,765,753; 3,767,307; 3,767,310; 3,776,636; 3,819,270; 3,837,731; 3,838,912; 3,840,291; 3,840,298; 3,842,253; 3,842,254; 3,842,713; 3,844,645; 3,844,658; 3,860,346; 3,862,357; 3,864,016; 3,865,464; 3,866,038; 3,867,009; 3,869,193; 3,869,195; 3,871,740; 3,881,801; 3,881,802; 3,891,849; 3,892,966.