# Flywheels Ø100–Ø200 with hex-nut rim pockets

> How is a flywheel with hex nut pockets in the rim laid out?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Rim of hex pockets at the nut's across-flats, one flat facing out, depth = nut thickness; pocket count a multiple of 6
- Page: https://xemstudio.com/objects/nut-pocket-flywheels/ · JSON: https://xemstudio.com/api/geometry?object=nut-pocket-flywheels · Plain text: https://xemstudio.com/objects/nut-pocket-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 rim of hex pockets, each at the nut's exact across-flats with one flat facing outward and as deep as the nut is thick, on a 1.5 mm floor; a nut sits flush with the face.
- Pocket counts are multiples of six: all, every other one, every third or one half can be filled and the wheel stays balanced, or one half only makes a counterweight opposite the crank pin.
- Rim thickness = nut thickness + 1.5; rim radial width = across-flats + 6. A 4 mm web with six round windows joins the rim to a hub Ø20 (Ø3 and Ø5 bore) or Ø22 (Ø8 bore), 4 mm taller than the rim.
- Each hub has a radial Ø2.5 hole (M3 tap drill) for a grub on the shaft's D-flat. Ø3 hubs exist on the Ø100 and Ø120 wheels only.

## 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-* |
| grub hole | Ø2.5 | M3 tap drill | designed | flywheel-* |

## Sizes

| OD | nut | pockets | pocket circle R | rim thickness | rim width | hub | bores |
|---|---|---|---|---|---|---|---|
| 100 | M8 | 12 | 40.5 | 8.3 | 19.0 | Ø20 / Ø22 × 12.3 | 3 / 5 / 8 |
| 120 | M10 | 12 | 49.0 | 9.9 | 22.0 | Ø20 / Ø22 × 13.9 | 3 / 5 / 8 |
| 120 | 3/8 in | 12 | 49.9 | 9.8 | 20.3 | Ø20 / Ø22 × 13.8 | 3 / 5 / 8 |
| 150 | M10 | 18 | 64.0 | 9.9 | 22.0 | Ø20 / Ø22 × 13.9 | 5 / 8 |
| 150 | M12 | 12 | 63.0 | 12.3 | 24.0 | Ø20 / Ø22 × 16.3 | 5 / 8 |
| 150 | 1/2 in | 12 | 62.5 | 12.6 | 25.1 | Ø20 / Ø22 × 16.6 | 5 / 8 |
| 200 | M12 | 18 | 88.0 | 12.3 | 24.0 | Ø20 / Ø22 × 16.3 | 5 / 8 |
| 200 | 1/2 in | 18 | 87.5 | 12.6 | 25.1 | Ø20 / Ø22 × 16.6 | 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 (19 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/nut-pocket-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

## How it fits

### Goes in or on
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/): Ø3 / Ø5 / Ø8 hub, M3 grub on the flat
- [Crank stands with a 625 pocket, 40 and 60 mm axis height](https://xemstudio.com/objects/crank-stands-625/): on the Ø5 shaft outside the stand

### Connects to
- [Hex nuts M8, M10, M12, 3/8 in and 1/2 in (flywheel weights)](https://xemstudio.com/objects/hex-nut-weights/): nut in each hex pocket, one flat outward

### Alternatives
- [Spoked flywheels Ø50 to Ø150 × 10](https://xemstudio.com/objects/spoked-flywheels/): plain spoked wheel

### Also needed
- [Set screws (grub screws), M3–M8 (ISO 4026)](https://xemstudio.com/objects/set-screws-metric/): M3 grub

## Questions

**How many nuts does the Ø150 flywheel hold?**

18 M10 nuts on the M10 wheel (R64), or 12 on the M12 and 1/2 in wheels.

**Can I fill only some pockets?**

Yes: pocket counts are multiples of six, so all, alternate, every third or one half all leave the wheel balanced, and one half only is a counterweight.

**Metric or inch nuts?**

The Ø120, Ø150 and Ø200 wheels come in 3/8 in and 1/2 in versions as well as M10 and M12.

## Fits with

- [Hex nuts M8, M10, M12, 3/8 in and 1/2 in (flywheel weights)](https://xemstudio.com/objects/hex-nut-weights/)
- [Spoked flywheels Ø50 to Ø150 × 10](https://xemstudio.com/objects/spoked-flywheels/)
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/)
- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/)
- [Counterweighted crank discs, Ø5 bore, 10 to 30 mm stroke](https://xemstudio.com/objects/counterweighted-crank-discs/)