The thread is the mechanical contract: what screws into what, at which pitch, and how far the glass sits from the sensor. M12, M8, CS, C, and the rest are not quality grades. They are families of holders. An M12 lens in a CS hole is not a clever adapter. It is a future support ticket.
In one sentence. Thread plus pitch plus back focal distance is the mount. Matching only the thread is how you get a lens that sits 2 mm too far from the die.
The common ones on Camemaker
- M12 / S-mount. Board cameras. Pitch is often 0.5 mm. Confirm it. A 0.35 mm "M12" exists and will cross-thread a standard holder.
- M8. Smaller still. Endoscopes and tiny modules. Do not assume M12 accessories.
- CS-mount. 12.5 mm flange-ish world. Security and many industrial boxes.
- C-mount. 17.5 mm. Bigger sensors, bigger glass, room for a real iris.
Camemaker also lists thread pitch and head OD. Those decide the holder drawing, not the brochure photo.
The jar-lid test
Two jars can both be "about 8 cm." Only one lid closes. Pitch and diameter are the lid. Back focal is whether the lid still seals when the gasket is a different thickness. You do not force it and call it compatible.
How to filter
In the lens library, Thread is the first mechanical cut. Then pitch. Then optical and mechanical BFL against the holder you actually have. Format and image circle still come before all of this if you want a picture, not only a screw that turns.