| Number | Name | Date | Kind |
|---|---|---|---|
| 2205433 | Paulsen | Jun 1940 | |
| 2222983 | Marcher | Nov 1940 | |
| 2482613 | Erickson | Sep 1949 | |
| 2875115 | Dusenbury | Feb 1959 | |
| 3874648 | King | Apr 1975 | |
| 3901500 | Gath | Aug 1975 | |
| 4118022 | Rayfield | Oct 1978 | |
| 4147338 | Gath | Apr 1979 |
| Entry |
|---|
| European Patent Application #79300735.2, Filed 4-30-79. |