This knob is used for manually rotating the spindle via the drive hub, allowing you to position it exactly where you want with a comfortable knurled grip. It has a diameter of about 3 in. and a thickness of 1 in., so most hand sizes will be able to hold it easily.

These are 3D-printed from PLA, designed to be durable while still being very light and small. The fit is intentionally loose to hopefully discourage it being left on when the machine is powered on and flying off.