# Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools

> What size displacer fits a 2 inch tri-clamp spool?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: 16 ga ASME BPE tube bores (1.5 in 34.8, 2 in 47.5, 3 in 72.9 mm) minus a designed radial gap of 0.6 / 0.75 / 1.0 mm (Senft, low-temperature-difference air engines)
- Page: https://xemstudio.com/objects/tri-clamp-displacer/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-displacer · Plain text: https://xemstudio.com/objects/tri-clamp-displacer/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**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 displacer is a closed cylinder that runs in the spool bore with a designed radial gap: 0.6 mm in the 1.5 in spool (Ø33.6 in Ø34.8), 0.75 mm in the 2 in (Ø46.0 in Ø47.5), 1.0 mm in the 3 in (Ø70.9 in Ø72.9). The gap is part of the design and is drawn as is.
- Lengths: 1.5 in 50 / 75 / 100, 2 in 60 / 90 / 120, 3 in 80 / 120 / 160 mm. Each length comes two ways: a hollow shell (1 mm wall, closed rounded end, 1.2 mm internal rings every 25 mm) with its end cap, and a solid body of the same diameter and length with a Ø3 centre hole and two 0.6 mm slots crossing on the axis through the full length, so the file is four quarter-segments around the centre hole.
- The shell's end cap has a spigot Ø(D − 2) × 3 that enters the shell, a Ø D × 1.5 flange, and a Ø16 × 6 boss with the Ø3 rod hole and a Ø2.5 radial hole for an M3 grub at 8 mm; the cap stands 10.5 mm overall. One cap file per spool size serves every length.
- The Ø3 rod is the displacer rod: it leaves through the displacer head or crank head on the cold end. Every hole that meets another part is in the Mating features table.

## 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 |
|---|---|---|---|---|
| displacer OD in the spool bore | bore − 2 × 0.6 / 0.75 / 1.0 | tri-clamp-spool bore | designed | displacer-* |
| cap spigot in the shell | shell bore | displacer shell | slide | displacer-cap-* |
| cap rod hole | Ø3 | Ø3 displacer rod (M3 grub) | slide | displacer-cap-* |
| cap grub hole | Ø2.5 | M3 tap drill | designed | displacer-cap-* |
| displacer-body rod bore | Ø3 | Ø3 displacer rod | slide | displacer-body-* |

## Sizes

| spool_in | bore_mm | displacer_od_mm | length_mm | radial_gap_mm |
|---|---|---|---|---|
| 1.5 | 34.8 | 33.6 | 50 | 0.6 |
| 1.5 | 34.8 | 33.6 | 75 | 0.6 |
| 1.5 | 34.8 | 33.6 | 100 | 0.6 |
| 2 | 47.5 | 46.0 | 60 | 0.75 |
| 2 | 47.5 | 46.0 | 90 | 0.75 |
| 2 | 47.5 | 46.0 | 120 | 0.75 |
| 3 | 72.9 | 70.9 | 80 | 1.0 |
| 3 | 72.9 | 70.9 | 120 | 1.0 |
| 3 | 72.9 | 70.9 | 160 | 1.0 |

## Where the files are

- Long Earth Society: [Tri-clamp Stirling engine builds](https://longearthsociety.com/engineering/) — web, video — LES site
- James R. Senft: [An Introduction to Low Temperature Differential Stirling Engines (displacer and gap design)](https://www.stirlingengine.com/) — book — Moriya Press (verify at link)
- Wikipedia: [Stirling engine](https://en.wikipedia.org/wiki/Stirling_engine) — web — CC BY-SA 4.0 (text)

## Free STEP/STL (27 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-displacer/index.json

- displacer-shell-1.5in-50: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-1.5in-50.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-1.5in-50.stl) — 1.5 in shell displacer Ø33.6 × 50 for the Ø34.8 bore (0.6 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-1.5in.stl) — 1.5 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-1.5in-50: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-1.5in-50.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-1.5in-50.stl) — 1.5 in solid displacer body Ø33.6 × 50 with a Ø3 rod bore on the axis
- displacer-shell-1.5in-75: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-1.5in-75.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-1.5in-75.stl) — 1.5 in shell displacer Ø33.6 × 75 for the Ø34.8 bore (0.6 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-1.5in.stl) — 1.5 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-1.5in-75: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-1.5in-75.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-1.5in-75.stl) — 1.5 in solid displacer body Ø33.6 × 75 with a Ø3 rod bore on the axis
- displacer-shell-1.5in-100: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-1.5in-100.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-1.5in-100.stl) — 1.5 in shell displacer Ø33.6 × 100 for the Ø34.8 bore (0.6 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-1.5in.stl) — 1.5 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-1.5in-100: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-1.5in-100.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-1.5in-100.stl) — 1.5 in solid displacer body Ø33.6 × 100 with a Ø3 rod bore on the axis
- displacer-shell-2in-60: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-2in-60.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-2in-60.stl) — 2 in shell displacer Ø46 × 60 for the Ø47.5 bore (0.75 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-2in.stl) — 2 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-2in-60: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-2in-60.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-2in-60.stl) — 2 in solid displacer body Ø46 × 60 with a Ø3 rod bore on the axis
- displacer-shell-2in-90: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-2in-90.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-2in-90.stl) — 2 in shell displacer Ø46 × 90 for the Ø47.5 bore (0.75 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-2in.stl) — 2 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-2in-90: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-2in-90.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-2in-90.stl) — 2 in solid displacer body Ø46 × 90 with a Ø3 rod bore on the axis
- displacer-shell-2in-120: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-2in-120.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-2in-120.stl) — 2 in shell displacer Ø46 × 120 for the Ø47.5 bore (0.75 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-2in.stl) — 2 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-2in-120: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-2in-120.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-2in-120.stl) — 2 in solid displacer body Ø46 × 120 with a Ø3 rod bore on the axis
- displacer-shell-3in-80: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-3in-80.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-3in-80.stl) — 3 in shell displacer Ø70.9 × 80 for the Ø72.9 bore (1.0 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-3in.stl) — 3 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-3in-80: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-3in-80.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-3in-80.stl) — 3 in solid displacer body Ø70.9 × 80 with a Ø3 rod bore on the axis
- displacer-shell-3in-120: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-3in-120.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-3in-120.stl) — 3 in shell displacer Ø70.9 × 120 for the Ø72.9 bore (1.0 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-3in.stl) — 3 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-3in-120: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-3in-120.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-3in-120.stl) — 3 in solid displacer body Ø70.9 × 120 with a Ø3 rod bore on the axis
- displacer-shell-3in-160: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-3in-160.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-shell-3in-160.stl) — 3 in shell displacer Ø70.9 × 160 for the Ø72.9 bore (1.0 mm radial gap), 1 mm wall, internal rings every 25 mm, closed rounded end
- displacer-cap-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-cap-3in.stl) — 3 in displacer end cap with Ø3 rod boss and M3 grub (Ø2.5 tapped) at 8 mm; one per displacer
- displacer-body-3in-160: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-3in-160.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-body-3in-160.stl) — 3 in solid displacer body Ø70.9 × 160 with a Ø3 rod bore on the axis

## How it fits

### Parts that fit it
- [Regenerator matrix disc Ø44 / Ø32 × 0.5 mm (mesh counts #40–#200)](https://xemstudio.com/objects/regenerator-mesh-disc/): matrix in the regenerative displacer's slots
- [Crank discs Ø30 for a Ø3 crankshaft, 10 to 20 mm stroke](https://xemstudio.com/objects/crank-discs-3mm-bore/): on the crank head's Ø3 shaft between the 623 towers
- [Displacer rods Ø2 × 60, 78, 100 and 180, Ø3 × 100, 150 and 200](https://xemstudio.com/objects/displacer-rods/): Ø3 rod in the displacer cap socket and the head's Ø3 bore

### Goes in or on
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/): Ø46 displacer in the Ø47.5 bore, 0.75 mm radial gap
- [Tri-clamp cups: closed-end spools (ferrule on a capped tube), 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-cups/): same 47.5 bore with the hot end closed

### Connects to
- [Tri-clamp displacer head: ISO 2852 cap with Ø3 rod bore and 4 mm barb, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-displacer-head/): Ø3 rod from the cap through the head's Ø3 bore
- [Tri-clamp crank head: ISO 2852 cap with Ø3 rod bore and two 623 towers, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-crank-head/): Ø3 rod through the crank head to a crank

### Alternatives
- [Tri-clamp regenerative displacer: Ø31.8, Ø44.5 and Ø69.9 with 12 slots, 1.5 mm gap](https://xemstudio.com/objects/tri-clamp-regenerative-displacer/): single-spool engine with the regenerator in the gap

### Also needed
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/): Ø3 displacer rod

## Questions

**What diameter displacer fits a 2 inch tri-clamp spool?**

Ø46.0 mm in the Ø47.5 bore, a 0.75 mm radial gap, in 60, 90 or 120 mm lengths.

**How much gap is there between the displacer and the spool?**

0.6 mm radial in the 1.5 in spool, 0.75 mm in the 2 in, 1.0 mm in the 3 in: a designed gap, drawn at that size.

**How does the rod attach to the displacer?**

Through the end cap: a Ø3 hole in a Ø16 × 6 boss, held by an M3 grub in a Ø2.5 radial hole 8 mm up the cap.

**Is there a solid version?**

Yes: each length also comes as one solid body of the same diameter and length (Ø × L), with a Ø3 centre hole and two 0.6 mm cross slots.

## Fits with

- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/)
- [Tri-clamp displacer head: ISO 2852 cap with Ø3 rod bore and 4 mm barb, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-displacer-head/)
- [Tri-clamp crank head: ISO 2852 cap with Ø3 rod bore and two 623 towers, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-crank-head/)
- [Tri-clamp regenerative displacer: Ø31.8, Ø44.5 and Ø69.9 with 12 slots, 1.5 mm gap](https://xemstudio.com/objects/tri-clamp-regenerative-displacer/)
- [Tri-clamp cups: closed-end spools (ferrule on a capped tube), 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-cups/)
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/)