# Retaining ring (DIN 471 pattern)

External retaining ring (circlip) for shafts, shaft diameters 10 to 34 mm, as the published FreeCAD-library models
draw them: the ring's outline with its lugs and lug holes, a flat plate of the ring's thickness.

## Geometry

The ring lies on the XY plane from z = 0 to its thickness s, the bore centred on the origin (shaft axis along Z), the
lugs toward +X. Each size's outline is the reference model's own, written in the recipe as a table (`RINGS`, in
`part.py`): lines and arcs (each arc by its ends and midpoint) and the two lug holes.

Measured on the models, mm (bore d3: the ring's inside arc, free state; extents: across the lugs (X) × across (Y)):

| d1 | s | d3 | Extents | Lug holes |
|---|---|---|---|---|
| 10 | 1 | 9.2966 | 14.54 × 12.3 | 1.5 |
| 12 | 1 | 11 | 16.06 × 14 | 1.7 |
| 14 | 1 | 12.8 | 18.5 × 16.4 | 1.7 |
| 16 | 1 | 14.7 | 20.6 × 18.34 | 1.7 |
| 18 | 1.2 | 16.6 | 22.9 × 20.5 | 2 |
| 20 | 1.2 | 18.6 | 25.2 × 22.8 | 2 |
| 22 | 1.2 | 20.6 | 27.6 × 25.2 | 2 |
| 24 | 1.2 | 22.1773 | 29.58 × 27.14 | 2 |
| 26 | 1.2 | 24.1999 | 31.8 × 29.3 | 2 |
| 28 | 1.5 | 25.9 | 33.8 × 31.1 | 2 |
| 30 | 1.5 | 27.9987 | 36.6 × 33.89 | 2 |
| 32 | 1.5 | 29.4739 | 38.34 × 35.57 | 2.5 |
| 34 | 1.5 | 31.6321 | 40.79 × 37.92 | 2.5 |

## Parameters

| Parameter | Meaning |
|---|---|
| `size` | shaft diameter d1, mm |
| `material` | `spring-steel` (STEVE `steel-c60e`, the closest grade to DIN 471's C75S) or `stainless` |

## Sources

DIN 471 gives the ring's thickness, bore, lug size and hole diameter but no drawing of the ring's outline between its
back and its lugs. **The geometry was measured from the published reference models** below: each model's largest
planar face gives the ring's plane, the thickness is the model's extent across it, and the outline is the OCCT section
at mid-thickness with every edge read exactly (line ends; each arc's ends and midpoint), rounded to 0.0001 mm; the
recipe re-draws it in its own code. Every preset is checked against its own model: bounding box within 0.05 mm (the
M10 model is stored tilted, so its oriented box is compared) and volume within 2 %.

- **FreeCAD-library**, `Mechanical Parts/Fasteners/RetainingRings/Metric/DIN471_CLASS_A_M<d1>RetainingRings.step` for
  d1 = 10 to 34 (commit 2e36ae32), by **nachotineo** (added 2015-10-11);
  https://github.com/FreeCAD/FreeCAD-library; licensed under
  [CC-BY-3.0](https://creativecommons.org/licenses/by/3.0/) (the library's licence for all its parts). Distributed by
  step.parts as `din471_retaining_ring_m<d1>` / `din471_external_retaining_ring_m<d1>`
  (https://www.step.parts), identical geometry. No endorsement by the author or the FreeCAD project is implied.

The models follow DIN 471's key dimensions closely but not exactly: their bores differ from DIN 471's d3 by up to
0.13 mm in some sizes (14, 18, 20, 22, 30, 32, 34). The recipe keeps the models' values; use DIN 471's table where
the groove fit matters. Simplifications: none beyond the models' own (sharp edges, free state).

Preset list: from the step.parts catalogue (MIT), see `library/NOTICE.md`.