Z-Axis Knob for Printrbot Simple

Got a Printrbot Simple but it needs a knob to turn the z-axis up and down for zeroing. It had to be something small, because there's not a lot of clearance around the screw on such a small machine. So here's a little knob that screws on the top! Should also fit any other 8mm threaded rods.

The hole in the center is 6.75mm, suitable for tapping to M8x1.25, but you want the knob to bind in place around the shaft -- so just hold the shaft with vise-grips and carefully thread the knob on with mod