# Cotter pin (simplified)

A simplified cotter pin (split pin) for assemblies, nominal sizes 1, 1.6, 2, 2.5, 3.2, 4 and 5 mm (the ISO 1234
sizes), any length.

## Geometry

Two round legs of the nominal diameter d, side by side (axes at x = ±e), along +Z from z = 0 to the length l, and a
round bar of diameter d along X, 2d long, centred on the origin, standing for the eye. Overall: 2d × d × (l + d/2).

| d | Legs and bar Ø | Leg axis offset e | Bar length |
|---|---|---|---|
| 1 | 1 | 0.35 | 2 |
| 1.6 | 1.6 | 0.56 | 3.2 |
| 2 | 2 | 0.7 | 4 |
| 2.5 | 2.5 | 0.875 | 5 |
| 3.2 | 3.2 | 1.12 | 6.4 |
| 4 | 4 | 1.4 | 8 |
| 5 | 5 | 1.75 | 10 |

## Parameters

| Parameter | Meaning |
|---|---|
| `size` | nominal size d (the hole diameter), mm |
| `length` | l, mm (from the eye's centre line to the leg ends) |
| `material` | `steel` (STEVE `steel-generic`) or `stainless` (`stainless-304`) |

## Sources

ISO 1234 gives d, a, b, c and l but not the eye's shape, and no maker publishes a dimensioned drawing of it: **the
geometry was measured from the published reference models** below (every face read: the legs' and the bar's
cylinder radii and axes; e = 0.35 d and the bar 2 d long in every size), and the recipe re-draws it in its own code.
Every preset is checked against its own model: bounding box within 0.05 mm and volume within 2 %.

- **step.parts**, `iso_1234_cotter_pin_d<d>_l<l>_simple` for d = 1 to 5 (https://www.step.parts, repository
  https://github.com/earthtojake/step.parts, commit c6113328, `catalog/step/`): step.parts' own "analytic simplified"
  models, original project material under the repository's **MIT** licence (© 2026 earthtojake; no third-party
  source is recorded for them in its THIRD_PARTY_NOTICES.md or catalogue).

Simplifications (the models'): the legs are full round rods of the nominal diameter (a real pin is a half-round wire
somewhat thinner than the hole), the eye is a straight bar instead of a loop, and there is no point or bent-out leg.
Use it as an envelope in assemblies, not for the wire's dimensions.

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