A fingerwheel for a M8 threaded rod (like the MakerBot Z rod), with space to add a M8 nut. I plan to add this to the CRASH Space MakerBot as a manual Z-axis control, and to use it for a leveling platform idea I'm working on.
Inspired by Antona's 4-Star Knob For M8 Nut (http://www.thingiverse.com/thing:3723), I used zignig's Finger Wheel OpenSCAD script (http://www.thingiverse.com/thing:3288), tweaked it a bit, then added a larger shaft and carved out space for the M8 nut.
Put this on a rod, lock a second nut next to it, and you can spin the rod all day without it unscrewing from the rod.
2) Press M8 nut into hole.
The nut will probably be very tight. You may need to clean up the inside of the hole a little bit. And you may need to use an arbor press (or bench vice or C clamp or whatever) to get it in. It should fit very tightly - you don't want it coming out.
Screw another M8 nut on to your threaded rod, then this. Counter rotate the two nuts together to lock everything in place. Will easily come off with a pair of wrenches, but won't unscrew until then.