[luka]

I recently IR modded (full mod) my DSLR and got Baader IR/UV-cut filter to block the IR.

The imaging setup consists of:
ED80 - Hotech SCA flattener - T-ring - Canon 1200D
and now the IR/UV-cut filter has to be screwed into the Hotech SCA flattener (on the ED80 side).

Both the IR/UV-cut filter and the flattener have standard 2" size with M48 threads... but they don't fit into each other.

The filter goes in about 1 turn and stops (it is not all the way in). Normally I would say that the threads have a different pitch but the filter fits nicely into several other M48 pieces I have and then other M48 pieces fit nicely into the flattener. Actually I can do a "full circle" - the filter fits into one of the spare adapters; which fits into another adapter; which fits into the flattener. Everything fits perfectly indicating that the threads are the same and that the filter should fit into the flattener. But it does not.

This is driving me nuts. Any ideas? Is it just sloppy tolerances? (all parts are new)