# L-Mount: 20 mm flange focal distance, 51.6 mm diameter

> What is the L-Mount flange focal distance and throat diameter?

- Category: Cameras & lenses › Lens mounts & filter threads
- Kind: Standard part
- Basis: Published numbers only (sources per row); no bayonet geometry is published, so no file
- Page: https://xemstudio.com/objects/l-mount/ · JSON: https://xemstudio.com/api/geometry?object=l-mount · Plain text: https://xemstudio.com/objects/l-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.
- Shared by the L-Mount Alliance makers; full-frame and APS-C lenses use the same mount.
- No file: the bayonet's lug widths, angles, depths and locking geometry are not published by the maker, so nothing is drawn. Only the published numbers are given.

## Sizes

| parameter | value | from |
|---|---|---|
| flange focal distance | 20 mm | L-Mount Alliance |
| throat / inner diameter | 51.6 mm (diameter) | L-Mount Alliance |
| coupling | bayonet | — |

## Where the files are

- L-Mount Alliance: [L-Mount overview (51.6 mm diameter, 20 mm flange distance)](https://l-mount.com/en/Overview) — web — Publisher's page; 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

## Questions

**What is the L-Mount flange distance?**

20 mm, with a 51.6 mm diameter (L-Mount Alliance).

## Fits with

- [Sony E-mount: 18 mm flange focal distance](https://xemstudio.com/objects/sony-e-mount/)
- [Canon RF mount: 20 mm flange focal distance, 54 mm diameter](https://xemstudio.com/objects/canon-rf-mount/)
- [Micro Four Thirds mount: 19.25 mm flange focal distance](https://xemstudio.com/objects/micro-four-thirds-mount/)