| Size I.D. (mm) | Item No. |
| 3 | RET-UC-30 |
| 3.5 | RET-UC-3.5 |
| 4 | RET-UC-4.0 |
| 4.5 | RET-UC-4.5 |
| 5 | RET-UC-5.0 |
| 5.5 | RET-UC-5.5 |
| 6 | RET-UC-6.0 |
| 6.5 | RET-UC-6.5 |
| 7 | RET-UC-7.0 |
| 7.5 | RET-UC-7.5 |
| 8 | RET-UC-8.0 |
| 8.5 | RET-UC-8.5 |
| 9 | RET-UC-9.0 |
| 9.5 | RET-UC-9.5 |
Note: Flat springs need to be customized