# Nut-weighted flywheels: Ø100–200 with hex pockets for M8, M10, M12, 3/8 and 1/2 in nuts

> How do I make a 3D-printed flywheel heavy enough for a Stirling engine?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Hex nut envelopes from ISO 4032 (M8 13 × 6.8, M10 16 × 8.4, M12 18 × 10.8) and ASME B18.2.2 finished hex (3/8 in 9/16 × 21/64, 1/2 in 3/4 × 7/16 in); pockets drawn at the nut's nominal across-corners (press fit; nut masses computed from the hex envelope in steel, weigh yours
- Page: https://xemstudio.com/objects/nut-weighted-flywheels/ · JSON: https://xemstudio.com/api/geometry?object=nut-weighted-flywheels · Plain text: https://xemstudio.com/objects/nut-weighted-flywheels/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

- A printed flywheel is too light to carry a Stirling through its cycle; Each wheel has a ring of hex pockets with one flat facing outward, so every nut sits the same way, flush with the face, and the rim holds it against centrifugal load.
- Pockets come in multiples of six, so you can fill all of them (maximum inertia, balanced), every other one (half the weight, still balanced), every third, or only one half (a counterweight: the half opposite the crank pin). Press the nuts in; a drop of CA or a strip of tape over the face holds them for good.
- Hub: Ø3 (Ø100 and Ø120 only: can engine, LTD and crank-head Ø3 shafts), Ø5 (625 crank stands, rhombic gears, the gamma and alpha crankshafts) or Ø8 (tri-clamp crank frame), with an M3 grub on the shaft's D-flat; no adapter needed.
- Sizing: a 2 in tri-clamp gamma on a tea light runs well on Ø150 with a full set of M10 nuts (18 nuts, ~190 g, about +7.6 kg·cm² at the rim); the can engine on Ø100 M8 half-filled; LTDs want the lightest wheel that keeps them turning (start half-filled and add). Print flat, 4 walls, 30 % infill; the nuts are the mass.
- LES: the flywheels on the engines.

## 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 |
|---|---|---|---|---|
| hub bore | Ø3 / Ø5 / Ø8 | D-flat crankshaft (M3 grub) | slide | flywheel-* |
| rim pockets | nut across-corners | hex nut, one flat outward | press | flywheel-* |

## Sizes

| od_mm | nut | pockets | pocket_radius_mm | rim_mm | nut_g_each | full_set_g | added_inertia_kg_cm2 | bores |
|---|---|---|---|---|---|---|---|---|
| 100 | M8 | 12 | 40.5 | 8.3 | 5.6 | 67 | 1.1 | 3 / 5 / 8 |
| 120 | M10 | 12 | 49.0 | 9.9 | 10.3 | 124 | 3.0 | 3 / 5 / 8 |
| 120 | 3/8 in | 12 | 49.9 | 9.8 | 7.8 | 93 | 2.3 | 3 / 5 / 8 |
| 150 | M10 | 18 | 64.0 | 9.9 | 10.3 | 186 | 7.6 | 5 / 8 |
| 150 | M12 | 12 | 63.0 | 12.3 | 16.0 | 192 | 7.6 | 5 / 8 |
| 150 | 1/2 in | 12 | 62.5 | 12.6 | 18.5 | 221 | 8.6 | 5 / 8 |
| 200 | M12 | 18 | 88.0 | 12.3 | 16.0 | 288 | 22.3 | 5 / 8 |
| 200 | 1/2 in | 18 | 87.5 | 12.6 | 18.5 | 332 | 25.4 | 5 / 8 |

## Where the files are

- ISO: [ISO 4032 Hexagon regular nuts (style 1)](https://www.iso.org/standard/72624.html) — standard — ISO (verify at link)
- ASME: [ASME B18.2.2 Nuts for general applications](https://www.asme.org/codes-standards/find-codes-standards/b18-2-2-nuts-for-general-applications-machine-screw-nuts-hex-square-hex-flange-coupling-nuts-(inch-series)) — standard — ASME (verify at link)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (24 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/nut-weighted-flywheels/index.json

- flywheel-100-m8-b3: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b3.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b3.stl) — Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø3 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm²
- flywheel-100-m8-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b5.stl) — Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø5 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm²
- flywheel-100-m8-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b8.stl) — Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø8 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm²
- flywheel-120-m10-b3: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b3.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b3.stl) — Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø3 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm²
- flywheel-120-m10-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b5.stl) — Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø5 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm²
- flywheel-120-m10-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b8.stl) — Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø8 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm²
- flywheel-120-3-8in-b3: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b3.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b3.stl) — Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø3 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm²
- flywheel-120-3-8in-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b5.stl) — Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø5 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm²
- flywheel-120-3-8in-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b8.stl) — Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø8 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm²
- flywheel-150-m10-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b5.stl) — Ø150 flywheel, 18 pockets for M10 hex nuts at R64.0 (one flat facing out), Ø5 hub with M3 grub, 9.9 thick rim; full set ≈ 186 g of nuts, +7.6 kg·cm²
- flywheel-150-m10-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b8.stl) — Ø150 flywheel, 18 pockets for M10 hex nuts at R64.0 (one flat facing out), Ø8 hub with M3 grub, 9.9 thick rim; full set ≈ 186 g of nuts, +7.6 kg·cm²
- flywheel-150-m12-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b5.stl) — Ø150 flywheel, 12 pockets for M12 hex nuts at R63.0 (one flat facing out), Ø5 hub with M3 grub, 12.3 thick rim; full set ≈ 192 g of nuts, +7.6 kg·cm²
- flywheel-150-m12-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b8.stl) — Ø150 flywheel, 12 pockets for M12 hex nuts at R63.0 (one flat facing out), Ø8 hub with M3 grub, 12.3 thick rim; full set ≈ 192 g of nuts, +7.6 kg·cm²
- flywheel-150-1-2in-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b5.stl) — Ø150 flywheel, 12 pockets for 1/2 in hex nuts at R62.5 (one flat facing out), Ø5 hub with M3 grub, 12.6 thick rim; full set ≈ 221 g of nuts, +8.6 kg·cm²
- flywheel-150-1-2in-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b8.stl) — Ø150 flywheel, 12 pockets for 1/2 in hex nuts at R62.5 (one flat facing out), Ø8 hub with M3 grub, 12.6 thick rim; full set ≈ 221 g of nuts, +8.6 kg·cm²
- flywheel-200-m12-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b5.stl) — Ø200 flywheel, 18 pockets for M12 hex nuts at R88.0 (one flat facing out), Ø5 hub with M3 grub, 12.3 thick rim; full set ≈ 288 g of nuts, +22.3 kg·cm²
- flywheel-200-m12-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b8.stl) — Ø200 flywheel, 18 pockets for M12 hex nuts at R88.0 (one flat facing out), Ø8 hub with M3 grub, 12.3 thick rim; full set ≈ 288 g of nuts, +22.3 kg·cm²
- flywheel-200-1-2in-b5: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b5.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b5.stl) — Ø200 flywheel, 18 pockets for 1/2 in hex nuts at R87.5 (one flat facing out), Ø5 hub with M3 grub, 12.6 thick rim; full set ≈ 332 g of nuts, +25.4 kg·cm²
- flywheel-200-1-2in-b8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b8.stl) — Ø200 flywheel, 18 pockets for 1/2 in hex nuts at R87.5 (one flat facing out), Ø8 hub with M3 grub, 12.6 thick rim; full set ≈ 332 g of nuts, +25.4 kg·cm²
- nut-m8: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-m8.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-m8.stl) — M8 hex nut, 13 across flats × 6.8: the flywheel weight
- nut-m10: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-m10.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-m10.stl) — M10 hex nut, 16 across flats × 8.4: the flywheel weight
- nut-m12: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-m12.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-m12.stl) — M12 hex nut, 18 across flats × 10.8: the flywheel weight
- nut-3-8in: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-3-8in.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-3-8in.stl) — 3/8 in hex nut, 14.29 across flats × 8.33: the flywheel weight
- nut-1-2in: [STEP](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-1-2in.step) · [STL](https://xemstudio.com/files/hardware/nut-weighted-flywheels/nut-1-2in.stl) — 1/2 in hex nut, 19.05 across flats × 11.11: the flywheel weight

## How it fits

### Goes in or on
- [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/): Ø3 / Ø5 / Ø8 D-flat shafts

### Connects to
- [Stirling linkage fittings: rod clevises, shaft adapter, 625 crank stands, Ø3 crank discs, rhombic frame heads](https://xemstudio.com/objects/stirling-linkage-fittings/): gamma crankshaft in the 625 stands
- [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/): crank frame's Ø8 shaft
- [Rhombic drive kit (Philips beta Stirling): twin crank gears, links, yokes, frame](https://xemstudio.com/objects/rhombic-drive-kit/): long Ø5 gear shaft
- [Alpha V-twin frame for two 10 mL syringes: frame, crank disc and con-rods sized so it actually runs](https://xemstudio.com/objects/alpha-v-twin-frame/): behind the boss
- [Can-engine printed kit: can caps, diaphragm clamps, displacer guides, crank stands, CD/platter hubs, syringe cradles](https://xemstudio.com/objects/can-engine-printed-kit/): Ø3 hub on the skewer

### Alternatives
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/): plain printed flywheels
- [CDs, DVDs and hard-drive platters as flywheels](https://xemstudio.com/objects/cd-dvd-and-drive-platters/): CD flywheel for the can engine

### Also needed
- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/): steel nuts for the pockets
- [Set screws (grub screws), M3–M8 (ISO 4026)](https://xemstudio.com/objects/set-screws-metric/): M3 grub in the hub

## Questions

**How do I add weight to a 3D-printed flywheel?**

Fill all pockets for inertia, alternate pockets for half, or one half only as a counterweight.

**How heavy should a Stirling flywheel be?**

For a 2 in tri-clamp gamma, Ø150 with a full set of 18 M10 nuts adds about 190 g and 7.6 kg·cm² of inertia; start there and remove nuts until it still carries through a cycle. Lighter wheels start faster; heavier ones run smoother.

**Metric or inch nuts?**

Either: the Ø120, Ø150 and Ø200 wheels come in 3/8 in and 1/2 in versions for US hardware-store nuts as well as M10 and M12.

## Fits with

- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/)
- [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/)
- [Counterweighted crank discs, crank webs and bolt-on counterweights](https://xemstudio.com/objects/counterweighted-cranks/)
- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/)
- [Stirling linkage fittings: rod clevises, shaft adapter, 625 crank stands, Ø3 crank discs, rhombic frame heads](https://xemstudio.com/objects/stirling-linkage-fittings/)
- [Set screws (grub screws), M3–M8 (ISO 4026)](https://xemstudio.com/objects/set-screws-metric/)