Just finished making this 360 degree rotator, so I can get my 314L+ camera aligned on the OAG which was not possible just using the adapters (and although possible with adding shims, still tricky).
Optical length is c. 6mm.
It also mounts a 31mm Astronomik ProPlanet 642 BP IR filter, which has a plain 3mm deep mounting ring. Most of the filter is not used of course, but there doesn't seem to be a cheeper small one of say 12.7mm.
Waiting on taper-face M3 grub-screws to arrive, hopefully by the weekend.
Best,
Susan.