The files available on the Reprap wiki don't work properly with the belts I got from McMaster Carr. Mine say "Gates Powergrip made in USA" on the side and they look different, visually, from the ones I've seen in pictures of Mendels. The build file clearly claims that .2" pitch belts will work in place of the 5mm belts it normally uses, but the timing pulleys I printed out weren't anywhere close to 5 teeth per inch. One was 6/in and one was 5.5/in. Since they weren't even the same pitch I figured maybe the files were improperly scaled or something. So, I resized them until they were the correct pitch, but the teeth are too thin/far apart and leave one or two steps of play.I'm trying to generate a new set of pulleys based on the dimensions of the belt I have. I was going to do the math myself, but Erik already did it...so yay! http://www.thingiverse.com/thing:1362It took a few iterations to get the teeth sized and spaced correctly. I'm not really sure why. I think there's something going on in Erik's script that tries to account for the pitch getting smaller as the teeth wrap around the timing pulley, which makes sense, but it seems to overcompensate. The belts are .2" pitch (5mm) but I had to tell the script they were more like 5.4mm.Oh yeah, and the script works in millimeters, BTW.Anywho, now there's no play when the belt meshes with the pulley. If you get yet another style of belt it shouldn't be at all hard for you to tweak an appropriate design out of the script. Just download openscad (it's free). Then open Erik's script (it's free). Follow the directions (they're free). Remember to uncomment the teardrop section at the bottom. Print out a test piece (mostly free). Figure out how far off it is from where it's supposed to be and adjust the script accordingly. Print out another one. Repeat.The script doesn't include a gap for a captive nut to compliment the set screw, but if you make the set screw hole the right size the plastic will hold it in place just fine.