customizable knob

Dear all,

this is a customizer of the nice knob created by blackboots (https://www.thingiverse.com/thing:3240063).

I have been modifying 3 items:
- added a printable backplate
- give the choice if the base shall be hollow or solid
- added the choice for one or more holes to allow more easily removing this part from the print-bed
- I always use just machine-screws when putting parts together (no hex-nuts..). So I increased the length of the inner hole to fit longer screws


thanks

christian