The 5001-0013 is an adjustment knob for the Major 5001 wire stripping machine, which can be used to replace the strip length or wire diameter. When facing the machine, it is located on the top right (yellow cap) or front center (blue cap). The yellow capped knob adjusts the wire diameter while the blue capped knob sets the stripping length.

Replacement Knob for 5001 Electric Wire Stripper