# T-mount (T2): M42 × 0.75 thread, 55 mm flange, thread rings

> What is the T-mount (T2) 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/t-mount-t2/ · JSON: https://xemstudio.com/api/geometry?object=t-mount-t2 · Plain text: https://xemstudio.com/objects/t-mount-t2/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.
- Telescopes, mirror lenses and microscope adapters end in a male M42 × 0.75 thread; a camera-specific T-ring carries the female thread and sets the 55 mm to the image plane.
- Not interchangeable with M42 × 1 (M42 screw mount).

## Sizes

| parameter | value | from |
|---|---|---|
| flange focal distance | 55 mm | T-mount (Wikipedia); Flange focal distance table |
| throat / inner diameter | not published in a source I could verify (left out) | — |
| thread | M42 × 0.75 | standard |
| major Ø D | 42.000 mm | standard |
| pitch P | 0.75 mm | standard |
| pitch Ø D2 (basic) | 41.513 mm | ISO 68-1 basic profile |
| minor Ø D1 (basic) | 41.188 mm | ISO 68-1 basic profile |
| files | male and female ring sections, 8 turns, basic profile | — |

## Where the files are

- Wikipedia: [T-mount: M42 x 0.75 thread, 55 mm flange focal distance](https://en.wikipedia.org/wiki/T-mount) — web — CC BY-SA 4.0 (text); dimensions are facts
- 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/t-mount-t2/index.json

- m42x0-75-male-ring: [STEP](https://xemstudio.com/files/hardware/t-mount-t2/m42x0-75-male-ring.step) · [STL](https://xemstudio.com/files/hardware/t-mount-t2/m42x0-75-male-ring.stl) — M42 × 0.75 (T2) external thread ring section: ISO 68-1 basic profile, major Ø42, pitch Ø41.513, minor Ø41.188, pitch 0.75; 6 long (8 turns), bore Ø37.188 (wall is a design choice); exact nominal, no tolerance
- m42x0-75-female-ring: [STEP](https://xemstudio.com/files/hardware/t-mount-t2/m42x0-75-female-ring.step) · [STL](https://xemstudio.com/files/hardware/t-mount-t2/m42x0-75-female-ring.stl) — M42 × 0.75 (T2) internal thread ring section: ISO 68-1 basic profile, minor Ø41.188, pitch Ø41.513, major Ø42, pitch 0.75; 6 long (8 turns), outside Ø46 (design choice); exact nominal, no tolerance

## Questions

**What thread is a T2 / T-mount?**

M42 × 0.75 (42 mm, 0.75 mm pitch), 55 mm flange focal distance.

## Fits with

- [M42 screw mount (M42 × 1): 45.46 mm flange, thread rings](https://xemstudio.com/objects/m42-screw-mount/)
- [C-mount (1-32 UN): 17.526 mm flange, thread rings; CS-mount](https://xemstudio.com/objects/c-mount/)
- [Lens filter threads: M40.5 × 0.5 to M112, pitch table and thread rings](https://xemstudio.com/objects/lens-filter-threads/)