# Leaf hub collars: Ø12 and Ø18 bore, M3 grub

> How is a flexure leaf's hub held on its rod?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Design values of the free-piston generator; M3 grub (ISO 4026) in an Ø2.5 tapped hole
- Page: https://xemstudio.com/objects/fpse-hub-collars/ · JSON: https://xemstudio.com/api/geometry?object=fpse-hub-collars · Plain text: https://xemstudio.com/objects/fpse-hub-collars/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- The leaf's hub is clamped axially between a shoulder and a collar (leaf B: the displacer cap's boss and one Ø20 collar) or between two collars (leaves C and D on the Ø18 tube rod). Each collar holds with one M3 × 4 grub.
- Fit: the collar bores slide on the rod or tube and are held by the grub.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| bore | Ø12 / Ø18 | displacer rod / tube rod (M3 grub) | slide | all |
| grub hole | Ø2.5 | M3 tap drill | designed | all |

## Sizes

| collar | od_mm | bore_mm | h_mm |
|---|---|---|---|
| displacer | 20 | 12 | 5 |
| piston | 28 | 18 | 5 |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/fpse-hub-collars/index.json

- fpse-collar-12x20: [STEP](https://xemstudio.com/files/hardware/fpse-hub-collars/fpse-collar-12x20.step) · [STL](https://xemstudio.com/files/hardware/fpse-hub-collars/fpse-collar-12x20.stl) — collar Ø20 × 5, Ø12 bore, M3 tapped radial hole (Ø2.5): clamps leaf B's hub on the displacer rod against the cap's boss
- fpse-collar-18x28: [STEP](https://xemstudio.com/files/hardware/fpse-hub-collars/fpse-collar-18x28.step) · [STL](https://xemstudio.com/files/hardware/fpse-hub-collars/fpse-collar-18x28.stl) — collar Ø28 × 5, Ø18 bore, M3 tapped radial hole (Ø2.5): two per piston leaf, either side of its hub on the tube rod

## Questions

**How many?**

One Ø12 (leaf B) and four Ø18 (leaves C and D).

## Fits with

- [Tri-clamp flexure leaf: spiral planar spring clamped in a 2 in joint like a gasket (displacer and piston)](https://xemstudio.com/objects/tri-clamp-flexure-leaf/)
- [Build list: Free-piston Stirling generator, 2 in tri-clamp (pressurised, linear alternator)](https://xemstudio.com/objects/list-fpse-generator-2in/)