# Stirling linkage fittings: rod clevises, shaft adapter, 625 crank stands, Ø3 crank discs, rhombic frame heads

> What small fittings connect a Stirling engine's rods, cranks, flywheel and rhombic drive together?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: The Ø3 rod / Ø5 shaft / 623-625-608 bearing / M3 conventions used across the shelf; rhombic kit plates 80 × 50 with 625 pockets on 32 mm centres and M3 holes at (±20, −15)
- Page: https://xemstudio.com/objects/stirling-linkage-fittings/ · JSON: https://xemstudio.com/api/geometry?object=stirling-linkage-fittings · Plain text: https://xemstudio.com/objects/stirling-linkage-fittings/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- These are the parts that were missing between the kits: a plain Ø3 displacer rod had no way to take a con-rod (rod clevis: grub on the rod, 623 end on its pin); the Ø100 flywheel has a Ø8 bore and the gamma crankshaft is Ø5 (shaft adapter); the can-engine stands carry 623s but the gamma shaft needs 625s (crank stands); the crank head's towers take a Ø3 crankshaft and no disc had a Ø3 bore (crank discs b3); the rhombic gear plates had nothing to stand on (rhombic frame head).
- Gamma, 2 in, crank on the base plate: displacer rod Ø3 → rod-clevis-3mm → conrod-50 → cw-crank-disc on a Ø5 shaft in two crank-stand-625-h60 → shaft-adapter-5-to-8 → flywheel-100. Piston side: crosshead-8mm-rod3 (its own clevis) → conrod-40 → second crank disc 90° behind.
- Gamma, crank on the head: head-crank-2in (623 towers, Ø3 shaft) + crank-disc-b3 + conrod-40 to a rod clevis; flywheel-50 (Ø5 bore) needs a Ø3 → Ø5 bushing: use bushing-3x5x6 from the bearing housings entry.
- Beta, rhombic, 2 in: -rod piston + piston plug + 5 mm tube rod → yoke-lower-piston; displacer Ø3 rod through the tube → yoke-upper-displacer; gear frame plates on the rhombic frame head, 625s in the plates, Ø5 shafts, gears meshed 180° apart. Gear axes 70 mm above the ferrule face so the lower yoke clears the plug stub at bottom dead centre (yoke travel 32–48 mm below the gear line).
- Rhombic plates now specify 625 bearings (the earlier note said 623; the gears have Ø5 bores).
- LES: the bits between the kits.
- Fits are designed in: every hole is the mating part's size plus the clearance for the joint (press 0, slide +0.2, running pin +0.3, bearing / magnet / nut pocket +0.2, large sleeve +0.3 mm on diameter), so the parts print and go together as they are, in any material. Tapped holes are 2.5 mm for M3.

## Sizes

| spool | part | use |
|---|---|---|
| 1.5 | rhombic head | gear axes 70 mm above face; plates on M3 × 10 |
| 2 | rhombic head | gear axes 70 mm above face; plates on M3 × 10 |
| 3 | rhombic head | gear axes 70 mm above face; plates on M3 × 10 |
| any | rod-clevis-3mm | displacer rod → con-rod (623 end on the Ø3 pin) |
| any | rod-clevis-5mm-tube | tube piston rod → con-rod |
| any | shaft-adapter-5-to-8 | Ø8 flywheel on Ø5 crank |
| any | crank-stand-625 | 40 / 60 mm axis height, 625 bearing |
| any | crank-disc-b3 | for a Ø3 crankshaft: the crank head's 623 towers or the can engine's skewer |

## Where the files are

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

## Free STEP/STL (11 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/stirling-linkage-fittings/index.json

- rod-clevis-3mm: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rod-clevis-3mm.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rod-clevis-3mm.stl) — clevis for a Ø3 displacer or piston rod: Ø3 socket 12 deep with a tapped M3 grub, 5.2 mm gap, Ø3 pin: takes a con-rod's 623 end
- rod-clevis-5mm-tube: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rod-clevis-5mm-tube.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rod-clevis-5mm-tube.stl) — clevis for the 5 mm tube piston rod: Ø5 socket with a tapped M3 grub, 5.2 mm gap, Ø3 pin
- shaft-adapter-5-to-8: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/shaft-adapter-5-to-8.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/shaft-adapter-5-to-8.stl) — Ø5 → Ø8 shaft adapter × 20 with two M3 grubs: puts a Ø8-bore flywheel (Ø80–150) on a Ø5 crankshaft
- crank-stand-625-h40: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-stand-625-h40.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-stand-625-h40.stl) — crank stand, Ø5 shaft axis 40 mm up, Ø16 pocket for a 625 bearing (H7/m6), slotted feet 2 × M3 at 42 mm (print two; fits the gamma base plate slots)
- crank-stand-625-h60: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-stand-625-h60.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-stand-625-h60.stl) — crank stand, Ø5 shaft axis 60 mm up, Ø16 pocket for a 625 bearing (H7/m6), slotted feet 2 × M3 at 42 mm (print two; fits the gamma base plate slots)
- crank-disc-b3-stroke10: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-disc-b3-stroke10.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-disc-b3-stroke10.stl) — crank disc Ø30 for a Ø3 crankshaft (the crank head's 623 towers), pin at 5.0 mm (10 mm stroke), M3 grub
- crank-disc-b3-stroke15: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-disc-b3-stroke15.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-disc-b3-stroke15.stl) — crank disc Ø30 for a Ø3 crankshaft (the crank head's 623 towers), pin at 7.5 mm (15 mm stroke), M3 grub
- crank-disc-b3-stroke20: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-disc-b3-stroke20.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/crank-disc-b3-stroke20.stl) — crank disc Ø30 for a Ø3 crankshaft (the crank head's 623 towers), pin at 10.0 mm (20 mm stroke), M3 grub
- rhombic-frame-head-1.5in: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rhombic-frame-head-1.5in.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rhombic-frame-head-1.5in.stl) — 1.5 in rhombic frame head: ISO 2852 cap face, pedestal, two uprights 24 mm apart with 2 × M3 at ±20 mm, 55 mm above the face, matching the rhombic gear frame plates' mounting holes; gear axes land 70 mm above the face
- rhombic-frame-head-2in: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rhombic-frame-head-2in.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rhombic-frame-head-2in.stl) — 2 in rhombic frame head: ISO 2852 cap face, pedestal, two uprights 24 mm apart with 2 × M3 at ±20 mm, 55 mm above the face, matching the rhombic gear frame plates' mounting holes; gear axes land 70 mm above the face
- rhombic-frame-head-3in: [STEP](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rhombic-frame-head-3in.step) · [STL](https://xemstudio.com/files/hardware/stirling-linkage-fittings/rhombic-frame-head-3in.stl) — 3 in rhombic frame head: ISO 2852 cap face, pedestal, two uprights 24 mm apart with 2 × M3 at ±20 mm, 55 mm above the face, matching the rhombic gear frame plates' mounting holes; gear axes land 70 mm above the face

## How it fits

### Goes in or on
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/): rhombic frame head clamps on its ferrule
- [Gamma frame: base plates for tri-clamp engines, rocker beam and pivot post](https://xemstudio.com/objects/gamma-base-plate-and-beam/): crank stands bolt into the base plate slots

### Connects to
- [Nut-weighted flywheels: Ø100–200 with hex pockets for M8, M10, M12, 3/8 and 1/2 in nuts](https://xemstudio.com/objects/nut-weighted-flywheels/): Ø5-hub flywheel on the crank stands' shaft
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/): con-rods onto the clevises; flywheel on the 5→8 adapter
- [Counterweighted crank discs, crank webs and bolt-on counterweights](https://xemstudio.com/objects/counterweighted-cranks/): crank discs on the shaft in the 625 stands
- [Rhombic drive kit (Philips beta Stirling): twin crank gears, links, yokes, frame](https://xemstudio.com/objects/rhombic-drive-kit/): gear plates onto the rhombic frame head

### Also needed
- [Stirling shafts and rods: Ø3 rods, Ø5 / Ø8 D-flat crankshafts, Ø5 tube rods, Ø3 pins, thrust spacers](https://xemstudio.com/objects/stirling-shafts-and-rods/): Ø5 D-flat crankshaft, Ø3 pins, spacers
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/): 625 in the stands, 623 in the con-rods
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/): Ø3 clevis and crank pins
- [Set screws (grub screws), M3–M8 (ISO 4026)](https://xemstudio.com/objects/set-screws-metric/): M3 grubs
- [Shafts, D-flats, set-screw collars, E-clips (DIN 6799) and circlips (DIN 471)](https://xemstudio.com/objects/shaft-collars-clips-and-shafts/): Ø5 crankshaft

## Questions

**How do I connect a plain 3 mm displacer rod to a connecting rod?**

Rod clevis: its Ø3 socket (H7/h6) slides on the rod and an M3 grub locks it; the con-rod's 623 end sits in the 5.2 mm gap on a Ø3 pin.

**The flywheel has an 8 mm bore and my crankshaft is 5 mm. What now?**

The Ø5 → Ø8 shaft adapter: a 20 mm sleeve with two grubs, one on the shaft and one under the flywheel's set screw.

**How does the rhombic drive attach to a tri-clamp spool?**

The rhombic frame head clamps on the spool's open ferrule like any cap; its two uprights take the gear frame plates on M3 screws, putting the gear axes 70 mm above the face.

## Fits with

- [Tri-clamp power pistons and crank linkage: full-bore ring-less pistons, con-rods, crank webs and a clamp-on crank frame for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-power-pistons/)
- [Tri-clamp displacers and engine heads: 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacers-and-heads/)
- [Rhombic drive kit (Philips beta Stirling): twin crank gears, links, yokes, frame](https://xemstudio.com/objects/rhombic-drive-kit/)
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/)
- [Counterweighted crank discs, crank webs and bolt-on counterweights](https://xemstudio.com/objects/counterweighted-cranks/)
- [Power cylinder liners, piston blanks, crosshead and guide (the non-syringe power piston)](https://xemstudio.com/objects/power-cylinder-piston-crosshead/)
- [Gamma frame: base plates for tri-clamp engines, rocker beam and pivot post](https://xemstudio.com/objects/gamma-base-plate-and-beam/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [Shafts, D-flats, set-screw collars, E-clips (DIN 6799) and circlips (DIN 471)](https://xemstudio.com/objects/shaft-collars-clips-and-shafts/)
- [Bearing housings and linear supports: KP08, KFL08, SK8, SC8UU, V-wheels, sleeve bushings](https://xemstudio.com/objects/bearing-housings-and-rod-supports/)
- [Clevis pins, R-clips, cotter pins, clevises, universal joint, rod ends (heim joints)](https://xemstudio.com/objects/pins-clevises-and-joints/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)