# Clearance-seal pistons Ø48.00 × 34 for a bored 2 in spool: rod (gamma) and gland (beta)

> What piston goes in a bored and honed 2 in tri-clamp spool?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Design values; leakage from plane Poiseuille flow in the clearance (Hagen–Poiseuille)
- Page: https://xemstudio.com/objects/stirling-clearance-seal-pistons/ · JSON: https://xemstudio.com/api/geometry?object=stirling-clearance-seal-pistons · Plain text: https://xemstudio.com/objects/stirling-clearance-seal-pistons/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

- Ø48.00 × 34, no rings: the ground OD in the honed Ø48.00 bore is the seal. It is driven through a rod and a crosshead guided outside the cylinder, so it carries no side load and keeps its clearance.
- Gamma piston: the Ø8 rod screws into the boss and is locked with an M8 nut on the boss end.
- Beta piston: the displacer rod passes through a 6 × 10 × 10 sleeve bushing at the crown (its gland), and the hollow Ø10 piston rod screws into the boss until it bottoms.
- Leakage loss in the cycle model (charged air, 600 rpm): 0.44 / 1.50 / 3.54 W at 10 / 15 / 20 µm radial clearance on the gamma.

## 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 |
|---|---|---|---|---|
| OD | Ø48.00 × 34 | honed bore Ø48.00 (clearance seal) | run | all |
| rod socket | M8 tapped (Ø6.8) z 8–20 | Ø8 rod, M8 end | designed | piston-48-gamma* |
| gland seat | Ø10 × 10 at the crown | 6 × 10 × 10 sleeve bushing | press | piston-48-beta* |
| tube socket | M10 × 1 tapped (Ø9.0) z 14–30 | hollow rod, M10 × 1 end | designed | piston-48-beta* |

## Sizes

| part | od_mm | length_mm | rod |
|---|---|---|---|
| piston-48-gamma-m8 | 48.0 | 34.0 | M8 socket |
| piston-48-beta-gland | 48.0 | 34.0 | gland + M10 × 1 socket |

## Where the files are

- Wikipedia: [Hagen–Poiseuille equation: annular clearance leakage Q = π D δ³ Δp / 12 μ L](https://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation) — web — CC BY-SA 4.0 (text)
- 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/stirling-clearance-seal-pistons/index.json

- piston-48-gamma-m8: [STEP](https://xemstudio.com/files/hardware/stirling-clearance-seal-pistons/piston-48-gamma-m8.step) · [STL](https://xemstudio.com/files/hardware/stirling-clearance-seal-pistons/piston-48-gamma-m8.stl) — clearance-seal piston Ø48.00 × 34: crown 6, skirt 3, boss Ø18 with an M8 tapped (Ø6.8) socket z 8–20 for the rod
- piston-48-beta-gland: [STEP](https://xemstudio.com/files/hardware/stirling-clearance-seal-pistons/piston-48-beta-gland.step) · [STL](https://xemstudio.com/files/hardware/stirling-clearance-seal-pistons/piston-48-beta-gland.stl) — clearance-seal piston Ø48.00 × 34 for a beta: Ø10 × 10 gland seat at the crown (6 × 10 × 10 bushing, the displacer rod's gland), Ø7 on, M10 × 1 tapped (Ø9.0) socket z 14–30 for the hollow rod

## Questions

**What clearance?**

The fit class is a running fit to the honed bore; the leakage table shows what 10, 15 and 20 µm radial cost.

## Fits with

- [2 in × 3 in spool with the bore finished Ø48.00 (bored and honed power cylinder)](https://xemstudio.com/objects/tri-clamp-spool-bored-honed/)
- [Crosshead yokes with a Ø5 stub wrist pin: Ø6, Ø8 and hollow Ø10 rods](https://xemstudio.com/objects/stirling-crosshead-yokes/)
- [Build list: Tri-clamp horizontal gamma generator, 2 in, chargeable](https://xemstudio.com/objects/list-tri-clamp-horizontal-gamma/)
- [Build list: Tri-clamp charged beta, 2 in](https://xemstudio.com/objects/list-tri-clamp-charged-beta/)