| Number | Name | Date | Kind |
|---|---|---|---|
| 3015177 | Hembd et al. | Jan 1962 | |
| 3015897 | Hopp | Jan 1962 | |
| 3189187 | Guyer, Jr. et al. | Jun 1965 | |
| 3208758 | Carlson et al. | Sep 1965 | |
| 4145840 | Davidson | Mar 1979 | |
| 4681329 | Contin | Jul 1987 | |
| 4718637 | Contin | Jan 1988 | |
| 5116023 | Contin | May 1992 |
| Entry |
|---|
| MDC Vacuum Products Corp., Product catalog, pp. 2, 326-329 1992. |
| Kimball Physics, Inc., Product catalog, pp. 1-2, & 5:1-5:14, 1994. |