# C-mount (1-32 UN): 17.526 mm flange, thread rings; CS-mount

> What is the C-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/c-mount/ · JSON: https://xemstudio.com/api/geometry?object=c-mount · Plain text: https://xemstudio.com/objects/c-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.
- Machine-vision, CCTV, cine and microscope cameras: 1 in diameter, 32 threads per inch, designated 1-32 UN 2A (ISO 10935, interfacing connection type C). The lens has the male thread.
- CS-mount uses the same thread with a 12.526 mm flange distance: a C lens fits a CS camera with a 5 mm spacer, a CS lens does not focus on a C camera.
- The Unified thread basic profile is the same 60° profile as ISO 68-1, so the same formulas apply with P = 25.4/32 = 0.79375 mm.

## Sizes

| parameter | value | from |
|---|---|---|
| flange focal distance | 17.526 mm (0.6900 in); CS-mount 12.526 mm | ISO 10935 via Wikipedia |
| throat / inner diameter | not published in a source I could verify (left out) | — |
| thread | 1-32 UN (2A) | standard |
| major Ø D | 25.400 mm | standard |
| pitch P | 0.79375 mm | standard |
| pitch Ø D2 (basic) | 24.884 mm | ISO 68-1 basic profile |
| minor Ø D1 (basic) | 24.541 mm | ISO 68-1 basic profile |
| files | male and female ring sections, 8 turns, basic profile | — |

## Where the files are

- Wikipedia (citing ISO 10935:2009): [C mount: 1-32 UN 2A thread, 17.526 mm flange focal distance; CS mount 12.526 mm](https://en.wikipedia.org/wiki/C_mount) — web — CC BY-SA 4.0 (text); dimensions are facts
- Wikipedia: [Unified Thread Standard (ASME B1.1): same 60° basic profile as ISO 68-1](https://en.wikipedia.org/wiki/Unified_Thread_Standard) — 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

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

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

- 1-32un-male-ring: [STEP](https://xemstudio.com/files/hardware/c-mount/1-32un-male-ring.step) · [STL](https://xemstudio.com/files/hardware/c-mount/1-32un-male-ring.stl) — 1-32 UN (C-mount) external thread ring section: ISO 68-1 basic profile, major Ø25.4, pitch Ø24.884, minor Ø24.541, pitch 0.79375; 6.35 long (8 turns), bore Ø20.541 (wall is a design choice); exact nominal, no tolerance
- 1-32un-female-ring: [STEP](https://xemstudio.com/files/hardware/c-mount/1-32un-female-ring.step) · [STL](https://xemstudio.com/files/hardware/c-mount/1-32un-female-ring.stl) — 1-32 UN (C-mount) internal thread ring section: ISO 68-1 basic profile, minor Ø24.541, pitch Ø24.884, major Ø25.4, pitch 0.79375; 6.35 long (8 turns), outside Ø29.4 (design choice); exact nominal, no tolerance

## Questions

**What thread is a C-mount?**

1-32 UN 2A: 1 in (25.4 mm) diameter, 32 TPI; flange focal distance 17.526 mm (CS: 12.526 mm).

## Fits with

- [T-mount (T2): M42 × 0.75 thread, 55 mm flange, thread rings](https://xemstudio.com/objects/t-mount-t2/)
- [Micro Four Thirds mount: 19.25 mm flange focal distance](https://xemstudio.com/objects/micro-four-thirds-mount/)
- [Lens filter threads: M40.5 × 0.5 to M112, pitch table and thread rings](https://xemstudio.com/objects/lens-filter-threads/)