1. W.L. Finlay, U.S. patent 2,614,041 (14 October 1952).
2. S.A. Herres and T.K. Redden, U.S. patent 2,645,575 (14 July 1953).
3. S.A. Herres and T.K. Redden, U.S. patent 2,718,465 (20 September 1955).
4. S.A. Herres and T.K. Redden, U.S. patent 2,740,711 (3 April 1956).
5. J.O. Brittain and P.D. Frost, U.S. patent 2,739,887 (27 May 1956).