| Nominal Size Inches | Approx. Size in mm |
| 1/8"(3mm) | 3.5-4mm |
| 5/32" (4mm) | 4-4.5mm |
| 3/16" (5mm) | 5-5.5mm |
| 1/4" (6mm) | 6-7.5mm |
| 5/16" (8mm) | 8-9mm |
| 3/8" (10mm) | 10-11mm |
| 1/2" (12mm) | 11.5-13mm |
| 9/16" (14mm) | 14-15mm |
| 5/8" (16mm) | 16-17.5mm |
| 11/16" (18mm) | 18-19mm |
| 3/4" (20mm) | 20-21.5mm |
| 13/16"(22mm) | 22-23.5mm |
| 1" (25mm) | 24.5-26.5mm |
| 1-1/4" (32mm) | 32-34mm |
Note: The larger number measures the OD (Outside Diameter) of the ring. The smaller numbers measure the ID (Inner Diameter) and CS (Cross Sectional Diameter) of the ring. The OD = ID + 2xCS. (Example: OD 10mm, ID 8MM, CS 1mm)