Screw-in round filters are not generally described as using a universal ISO metric screw-thread standard in the way general hardware fasteners are. In practice, there is a de facto photography standard: most modern photographic screw-in filters use a 0.75mm thread pitch, especially among Japanese manufacturers, which is why filters of the same diameter are usually interchangeable across brands.

The key size is the filter diameter (for example, 52mm, 67mm, 77mm), typically marked with the ⌀ symbol on the lens or filter. As long as the diameter matches, filters will often fit, but there can be occasional exceptions or tolerance differences between brands or older equipment.