1. L.E. Lancy, D.C. Kruse, U.S. Pat. 3,764,503, Oct. 9, 1973
2. C.E. Tirrell, U.S. Pat. 3,761,369, Sept. 25, 1973
3. A. Fujii, U.S. Pat. 3,948,738, Apr. 6, 1976
4. R.F. Ehrsam, J.L. Raymond, R.Z. Reath, U.S. Pat. 3,909,381, Sept. 30, 1975
5. H.C. Hicks, Jr., U.S. Pat. 4,073,708, Feb. 14, 1978