# M42 screw mount (M42 × 1): 45.46 mm flange, thread rings

> What is the M42 screw mount flange focal distance?

- Category: Cameras & lenses › Lens mounts & filter threads
- Kind: Standard part
- Basis: Published numbers only (sources per row); thread drawn at the ISO 68-1 basic profile
- Page: https://xemstudio.com/objects/m42-screw-mount/ · JSON: https://xemstudio.com/api/geometry?object=m42-screw-mount · Plain text: https://xemstudio.com/objects/m42-screw-mount/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Flange focal distance is the distance from the mount's reference face to the image plane; adapters and extension tubes must add exactly the difference between two mounts' flange distances to keep infinity focus.
- The lens carries the male M42 × 1 thread; the camera body the female one.
- Not the same as the T-mount (M42 × 0.75): the two look alike but the pitches differ and they do not screw together.

## Sizes

| parameter | value | from |
|---|---|---|
| flange focal distance | 45.46 mm | Flange focal distance table |
| throat / inner diameter | not published in a source I could verify (left out) | — |
| thread | M42 × 1 | standard |
| major Ø D | 42.000 mm | standard |
| pitch P | 1 mm | standard |
| pitch Ø D2 (basic) | 41.350 mm | ISO 68-1 basic profile |
| minor Ø D1 (basic) | 40.917 mm | ISO 68-1 basic profile |
| files | male and female ring sections, 8 turns, basic profile | — |

## Where the files are

- Wikipedia: [Flange focal distance (table of mounts)](https://en.wikipedia.org/wiki/Flange_focal_distance) — web — CC BY-SA 4.0 (text); dimensions are facts
- Bureau of Indian Standards (via Public.Resource.Org): [IS 4218 (Part 1):2001 ISO general purpose metric screw threads, basic profile (identical with ISO 68-1:1998): H = 0.866025404 P, 5H/8 = 0.541265877 P, 3H/8 = 0.324759526 P](https://law.resource.org/pub/in/bis/S01/is.4218.1.2001.pdf) — web — Public.Resource.Org (public law); dimensions are facts
- ISO: [ISO 68-1:1998 ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads](https://www.iso.org/standard/3707.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/m42-screw-mount/index.json

- m42x1-male-ring: [STEP](https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-male-ring.step) · [STL](https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-male-ring.stl) — M42 × 1 lens mount external thread ring section: ISO 68-1 basic profile, major Ø42, pitch Ø41.350, minor Ø40.917, pitch 1; 8 long (8 turns), bore Ø36.917 (wall is a design choice); exact nominal, no tolerance
- m42x1-female-ring: [STEP](https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-female-ring.step) · [STL](https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-female-ring.stl) — M42 × 1 lens mount internal thread ring section: ISO 68-1 basic profile, minor Ø40.917, pitch Ø41.350, major Ø42, pitch 1; 8 long (8 turns), outside Ø46 (design choice); exact nominal, no tolerance

## Questions

**What thread is M42?**

M42 × 1 (42 mm, 1 mm pitch), 45.46 mm flange focal distance.

**Does an M42 lens fit a T-mount?**

No: T-mount is M42 × 0.75, a different pitch.

## Fits with

- [T-mount (T2): M42 × 0.75 thread, 55 mm flange, thread rings](https://xemstudio.com/objects/t-mount-t2/)
- [Canon EF mount: 44 mm flange focal distance](https://xemstudio.com/objects/canon-ef-mount/)
- [Nikon F mount: 46.5 mm flange focal distance](https://xemstudio.com/objects/nikon-f-mount/)
- [Lens filter threads: M40.5 × 0.5 to M112, pitch table and thread rings](https://xemstudio.com/objects/lens-filter-threads/)