CDs, DVDs and hard-drive platters as flywheels — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/cd-dvd-and-drive-platters/  (CC BY 4.0)
Basis: ECMA-130 / ISO 9660 physical disc: Ø120 × 1.2 mm, Ø15 mm hole; hard-drive platters per the 3.5 in (95 mm) and 2.5 in (65 mm) form factors
Catalog version: 2026-10-20

Sizes: see table below
- CD/DVD/Blu-ray: Ø120.0 mm, 1.2 mm thick, Ø15.0 mm centre hole, 16 g polycarbonate. Mini CD Ø80. The hole is held to +0.1 mm, so a printed Ø14.9 hub press-fits.
- 3.5 in drive platter: Ø95 × 1.27 mm (some 0.8–1.0), Ø25 mm hole, aluminium (older, 30 g) or glass (newer, do not drill). 2.5 in platter: Ø65 × 0.8, Ø20 hole. Mirror-flat, perfectly balanced: a stack of three 3.5 in platters on the printed hub is a 90 g, Ø95 flywheel.
- The hubs in the can-engine kit take a CD (Ø15 bore) or a 3.5 in platter (Ø25) onto a 5 mm or 8 mm shaft with a set screw. Two CDs glued with a 1 mm spacer are stiffer than one.
- A CD flywheel is 16 g at Ø120: it stores as much energy as a Ø60 × 10 mm steel disc, which is why the can engine runs on it.

disc  dia_mm  thickness_mm  hole_mm  mass_g
CD / DVD  120  1.2  15  16
mini CD  80  1.2  15  7
3.5 in HDD platter  95  1.27  25  30
2.5 in HDD platter  65  0.8  20  7

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Compact disc — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Compact_disc
- Wikipedia: Hard disk drive platter — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Hard_disk_drive_platter
- Long Earth Society: Engine builds (videos and write-ups) — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/index.json
API: https://xemstudio.com/api/geometry?object=cd-dvd-and-drive-platters