Printrbot Simple Z-axis Knob, v2

I really liked the knob that owens made for the Z axis on the Printrbot Simple. When I downloaded his part, I discovered the hole didn't go all the way through, and the nut fit was very tight. So I created a new version that is just like his, but that fixes these two problems. I've also uploaded an IGES file for those with 3D CAD programs that can edit and modify such files.