# Damper envelope (dashpot / gas strut)

A dashpot or gas strut envelope for assemblies: a cylinder body and a piston rod, two bodies on one axis, any stroke.

## Geometry

Along +X from the origin: the body, Ø10, 30 + stroke long; the rod, Ø5, 50 + stroke long, on the same axis inside the
body and coming out at +X, 10 + stroke / 2 beyond it (its other end is stroke / 2 − 10 from the body's left end, so
for strokes under 20 mm it shows behind the body, as in the models).

| Stroke (models) | Body | Rod | Overall |
|---|---|---|---|
| 10 | 40 | 60 | 60 |
| 15 | 45 | 65 | 65 |
| 25 | 55 | 75 | 77.5 |
| 50 | 80 | 100 | 115 |
| 100 | 130 | 150 | 190 |

## Parameters

| Parameter | Meaning |
|---|---|
| `stroke` | mm |
| `material` | `unspecified` (no material assigned) or `steel` |

## Sources

These generic envelopes name no maker and no standard covers them. **The geometry was measured from the published
reference models** below (the cylinders of each model's two solids: diameters, ends), and every preset is checked
against its own models: bounding box within 0.05 mm and volume within 2 %.

- **step.parts**, `dashpot_stroke<s>_envelope` and `gas_strut_stroke<s>_envelope` for s = 10, 15, 25, 50, 100
  (https://www.step.parts, repository https://github.com/earthtojake/step.parts, commit c6113328, `catalog/step/`):
  step.parts' own models, original project material under the repository's **MIT** licence (© 2026 earthtojake).
  They name no material, so the presets have `material = "unspecified"`.

Simplifications (the models'): dashpots and gas struts share this one envelope; no end fittings, piston or seals; body
and rod are plain cylinders (two bodies, the rod inside the body).

Preset list: from the step.parts catalogue (MIT), see `library/NOTICE.md`; a stroke's dashpot and gas strut share
one preset.