| Number | Name | Date | Kind |
|---|---|---|---|
| 1552127 | Ellingson | Sep 1925 | |
| 2441843 | Raiff et al. | May 1948 | |
| 2599859 | Ogg | Jun 1952 | |
| 3290990 | Garlick | Dec 1966 | |
| 3682547 | Ratowsky | Aug 1972 | |
| 3728021 | Retzyl et al. | Apr 1973 | |
| 4160597 | Damm et al. | Jul 1979 |
| Number | Date | Country |
|---|---|---|
| 411372 | Jun 1934 | GBX |
| Entry |
|---|
| I.B.M. Technical Disclosure Bulletin vol. 10, No. 11, Apr. 1968, p. 1735. |
| E. L. Bailey Document Stop. |