Just a simple cap to screw into unused RMS or M25x0.75 thread microscope objective sockets. (If anyone wants M32, I can probably make that too) I printed them in PLA with 100 µm layers. Infill settings aren't really important. If you have trouble threading them in, you can try reducing the scale a tiny bit to make it easier. I included the Fusion 360 archive and a STEP file, though I used a custom thread profile so the f3d file may not work properly. The M25 version has not been tested so let me know if there are any issues.