ACME Nut 12-3 thread

thingiverse

This is a hex nut designed to fit snugly onto a 12-3 leadscrew, such as the one found on this surplus car seat adjuster motor: www.amazon.com/12Vdc-Right-Angle-Drive-Electric/dp/B005IR1NBA The nut screws onto the acme thread leadscrew with a reasonably close fit (no noticeable backlash). Initially, it fits securely but is easily removable by the 12V gearmotor. I actually wanted the nut to fit extremely tightly on the screw so that I could sandwich a pulley between two of these nuts tightened against it, securing the pulley firmly against the shaft and allowing it to turn as the shaft rotates. It needs some locktite or other adhesive to transmit significant torque effectively. Of course, my part is still made from ABS plastic, which is far from a metal nut. A single acme 12-3 metal nut costs around $75 from McMaster, so there's that. EDIT: after threading it on and off several times, my first attempt became quite loose on the shaft. I have now created an updated version "AcmeNut12-3-Tight" using 11.5 mm as the pitch diameter instead of 12.0 mm, and removing the unnecessary face bevel to gain a little extra thread length. This revised version required a wrench to thread onto the shaft initially. After moving it some, it can now be turned with fingers, but it is still quite tight. You'll likely want to use thick walls and high infill for added strength.