| Number | Name | Date | Kind |
|---|---|---|---|
| 3370362 | Dodson | Feb 1968 | A |
| 3932949 | King | Jan 1976 | A |
| 4860475 | Levy et al. | Aug 1989 | A |
| 5009602 | Chandler | Apr 1991 | A |
| 6252241 | Sarussi | Jun 2001 | B1 |
| Entry |
|---|
| Pasco Product Catalog 2000 pp. 152-153, Printed in USA. |
| Daedalon Experiments & Apparatus Catalog 2000-2001 pp. 55-57, No Publisher or Country given. |
| Phywe Catalog, No Date given. pp. 14 & 15. No Publisher or Country given. |
| Hearlihy & Company Technology Education Catalog 2000 pp. 38039, No Publisher or Country given. |