M42 bodycap
thingiverse
I adapted https://www.thingiverse.com/thing:1110599 to resize it to the proper width and thread pitch and change "43" on the back to "42". It fits perfectly, but I've also since found another M42 bodycap on thingiverse, so take a look and pick whichever you prefer: https://www.thingiverse.com/thing:2864923
Download Model from thingiverse
With this file you will be able to print M42 bodycap with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on M42 bodycap.