I have a 50mm diameter, 2mm thick unmounted optical glass filter that I want to attach to my camera. I haven't been able to find a resource that describes the size of the optical glass used in standard photo filters. Would a 52mm mounting house a 50mm filter? I could do this by trial and error but I'm hoping someone already knows the answer.
For such project, I would use a step-up ring (e.g. 49-52mm to maximize usable filter area, or 46-52mm to have more leeway during mounting). The glass is guaranteed to fit in the 52mm inner thread and slimmer part with outer thread is guaranteed to provide support for the glass. To fix the glass into mount and fill the remaining gap, I'd try out silicone sealant first.
Disclaimer: I have made some DIY equipment, but not fixed glass to metal.
The diameter of the thread on the back of a filter, and the diameter of its front thread (for stacking multiple filters) are almost always the same, however the inner design/diameter of the filter holder ring may differ between manufacturers.
Unfortunately this means it is a matter of trial and error to find a suitable filter mount.
Exact details are not published by manufacturers, because it is expected that a filter will remain in its original holder/frame.