IDB-RET-044
Machine elements · circlips · dowel & spring pins
Retaining rings & pins
Holding parts on a shaft or in a bore without threads — retaining rings (circlips), dowel and spring pins, and the grooves and holes they need.
Abstract
Retaining rings and pins are the small, standard machine elements that locate and retain parts without threads — fast to assemble, cheap, and standardised. Rings take axial load (hold a bearing on a shaft); pins take location and shear (align two parts, carry torque). Choosing and grooving them correctly avoids pop-outs and loose fits.
Section 1 frames the options. Section 2 is retaining rings (circlips). Section 3 is pins. Section 4 is selection by function. Section 5 is groove and hole design. Section 6 is failure modes and a checklist.
1.Retention and location options
- Retaining ring (circlip / snap ring): axial retention in a groovethe standard way to hold a bearing, gear or pulley on a shaft or in a bore.
- Dowel pin: precise location between two parts (press fit in a reamed hole).
- Spring (roll) pin: location/torque in forgiving holesself-retaining, cheap.
- Cotter / clevis pin: serviceable pivot or removable retention.
- Use a ring instead of a nut/snap-fit when you want fast, repeatable axial retention; use a pin when you need alignment or shear transfer.
2.Retaining rings (circlips)
| Ring type | Notes |
|---|---|
| External / internal (DIN 471 / 472) | tapered-section, installed with pliers; the default |
| E-clip | snaps onto a groove from the side; light loads, fast |
| Spiral (constant-section) | no lugs, 360° contact, clean OD, higher thrust |
| Self-locking / push-on | no groove needed; permanent, light loads |
| Reinforced / bowed | higher thrust or take-up of end play |
- Thrust capacity is limited by the ring dishing out of the groove and by groove wall yieldingheavily loaded joints want a spiral or reinforced ring and a sharp-cornered groove.
- Add a chamfer/lead-in so the ring expands over the shaft to the groove during assembly.
3.Pins
| Pin | Hole | Use |
|---|---|---|
| Dowel (ground) | reamed H7, press fit | precise location between parts |
| Spring (slotted/coiled) | drilled, forgiving | location + light torque, self-retaining |
| Clevis + cotter | clearance | removable pivot |
| Grooved | drilled | press-retained, no reaming |
| Taper | reamed taper | precise location + light torque |
| Cotter / split | clearance | secure a castle nut / clevis |
Dowels carry location and shear but not tension — don't rely on a dowel to clamp. Two dowels (not three) locate a part fully; use clearance on extra pins to avoid over-constraint.
4.Selection by function
- Axial retention → retaining ring (spiral/reinforced for high thrust).
- Precise location → two dowel pins (reamed H7) plus bolts for clamping.
- Torque / shear in a forgiving hole → spring or grooved pin.
- Serviceable pivot → clevis + cotter.
- Cheapest light-duty retention → e-clip or push-on.
5.Groove and hole design
- Ring grooves: use the standard groove diameter, width and corner radius for the ring (DIN 471/472 tables)an off-spec groove drops thrust capacity and lets the ring tilt. Keep the groove a sharp corner on the load side.
- Edge distance: leave enough shaft beyond the groove (margin) so the land doesn't shear out under thrust.
- Dowel holes: ream to H7 for the dowel's press fit; align-ream mating parts together for true location. Provide a blind-hole vent or use a relieved/ pull-out dowel for serviceability.
- Chamfers everywhere the ring or pin entersassembly damage and shaved grooves come from sharp lead-ins.
6.Failure modes and checklist
| Mode | Cause | Fix |
|---|---|---|
| Ring dishes / pops out | thrust > capacity, shallow groove | spiral/reinforced ring, deeper sharp groove, support face |
| Groove wall yields | soft shaft, high thrust | harder shaft, larger groove, spread the load |
| Pin shears | overload, undersized | larger/stronger pin, more pins, share load |
| Dowel hole wears / loosens | repeated load, clearance fit | reamed H7 press fit, harder parts, more dowels |
| Spring pin walks out | wrong size/hole | correct pin OD vs hole, double pin |
Checklist: axial retention or location? → ring (size for thrust; spiral/reinforced if high) or dowel/spring pin (size for shear) → use the standard groove (DIN 471/472) or reamed H7 hole → adequate edge distance and chamfers → don't over-constrain with extra dowels.