| Number | Date | Country | Kind |
|---|---|---|---|
| 3420016 | May 1984 | DEX |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2580486 | Vigmostad | Jan 1952 | |
| 3116087 | Baumann | Dec 1963 | |
| 3472551 | Pickles | Oct 1969 | |
| 3627377 | Pickles | Dec 1971 | |
| 4521055 | Fudala | Jun 1985 | |
| 4574658 | Abbott et al. | Mar 1986 |
| Entry |
|---|
| Product Engineering, Jul. 31, 1961, pp. 31-33. |