Retaining Ring (Snap Ring) Reference
Retaining rings hold components on shafts or in bores without threads, pins, or adhesives. They sit in a machined groove and provide a shoulder. The two main types are external (on a shaft) and internal (in a bore).
External Retaining Rings (Shaft Rings)
| Shaft Ø (in) | Ring Thickness (in) | Groove Ø (in) | Groove Width (in) | Thrust Capacity (lbs) |
|---|---|---|---|---|
| 3/16 | 0.015 | 0.170 | 0.017 | 150 |
| 1/4 | 0.025 | 0.226 | 0.027 | 400 |
| 5/16 | 0.025 | 0.284 | 0.027 | 530 |
| 3/8 | 0.035 | 0.340 | 0.038 | 1,050 |
| 1/2 | 0.042 | 0.456 | 0.046 | 1,700 |
| 5/8 | 0.042 | 0.572 | 0.046 | 2,210 |
| 3/4 | 0.050 | 0.688 | 0.054 | 3,350 |
| 1 | 0.050 | 0.928 | 0.054 | 4,600 |
| 1-1/4 | 0.062 | 1.166 | 0.068 | 7,200 |
| 1-1/2 | 0.062 | 1.406 | 0.068 | 8,800 |
| 2 | 0.075 | 1.879 | 0.082 | 14,000 |
Internal Retaining Rings (Housing Rings)
| Bore Ø (in) | Ring Thickness (in) | Groove Ø (in) | Groove Width (in) | Thrust Capacity (lbs) |
|---|---|---|---|---|
| 3/8 | 0.025 | 0.407 | 0.027 | 700 |
| 1/2 | 0.035 | 0.538 | 0.038 | 1,300 |
| 5/8 | 0.035 | 0.666 | 0.038 | 1,650 |
| 3/4 | 0.042 | 0.795 | 0.046 | 2,500 |
| 1 | 0.042 | 1.055 | 0.046 | 3,400 |
| 1-1/4 | 0.050 | 1.310 | 0.054 | 5,100 |
| 1-1/2 | 0.050 | 1.560 | 0.054 | 6,200 |
| 2 | 0.062 | 2.060 | 0.068 | 10,000 |
Groove Design Notes
- Groove corners: Sharp corners (max 0.005″ radius) are required for the ring to seat properly. Don’t chamfer or break the groove edges.
- Groove surface finish: 63 µin Ra or better. Burrs will prevent proper seating.
- Ring protrusion: The ring must protrude enough from the groove to provide a shoulder. Check the assembled ring cross-section in the catalog.
- Plier holes: External rings have holes for expanding pliers; internal rings have holes for compressing pliers. Don’t mix up the tools.
- Stress concentration: The groove creates a severe stress riser on the shaft. See Stress Concentration Factors — Kt can be 3.0+ for retaining ring grooves under bending.
When NOT to Use Retaining Rings
- High thrust loads — retaining rings have limited axial capacity. For heavy loads, use a threaded nut, shoulder, or clamp collar.
- Rotating loads at the groove — the groove is a fatigue-critical stress riser. If the shaft bending stress is high at the groove location, consider relocating the ring or using a different retention method.
- Vibration environments — rings can pop out of grooves under extreme vibration. Use a spiral ring or locking ring instead.
Related: Stress Concentration Factors | Shaft Design | Press Fit Chart