Hex nuts M8, M10, M12, 3/8 in and 1/2 in (flywheel weights) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/hex-nut-weights/  (CC BY 4.0)
Basis: ISO 4032 (M8, M10, M12) and ASME B18.2.2 finished hex (3/8, 1/2 in) envelopes; bore at the thread major Ø
Catalog version: 2026-10-20

Sizes: see table below
- Hex nut envelopes: across flats × thickness, across corners, and a bore at the thread major Ø (thread not drawn).
- M8 13 × 6.8 (AC 15.01); M10 16 × 8.4 (18.48); M12 18 × 10.8 (20.78); 3/8 in 14.29 × 8.33 (16.50); 1/2 in 19.05 × 11.11 (22.00).
- Each sits in the matching flywheel pocket with one flat facing outward, flush with the rim face.

file  thread  across flats  across corners  thickness  bore
nut-m8  M8  13.0  15.01  6.8  8.0
nut-m10  M10  16.0  18.48  8.4  10.0
nut-m12  M12  18.0  20.78  10.8  12.0
nut-3-8in  3/8 in  14.29  16.5  8.33  9.53
nut-1-2in  1/2 in  19.05  22.0  11.11  12.7

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- ISO: ISO 4032 Hexagon regular nuts (style 1) — standard — ISO [verify license at link] — https://www.iso.org/standard/72624.html
- ASME: ASME B18.2.2 Nuts for general applications — standard — ASME [verify license at link] — 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)
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 5 parts): https://xemstudio.com/files/hardware/hex-nut-weights/index.json
API: https://xemstudio.com/api/geometry?object=hex-nut-weights