Simple to print, 10mm spacer for M42 lens mount. Inside screw has a lower tolerance, so you'll need a sand paper, or bit of force on first few uses. I used the dumber way and have a suggestion. Screw it on lens first. It'll save you a 40 minutes of strugle of getting it off the camera. Trust me, I know, what i'm talking about. 

Also a friendly reminder of adding one stop of light, when shooting with.