About this 3D model

I wanted to make my own knob for a rotary encoder, but couldn't figure out how to make the "D" shaped mounting hole in my knob. So this is a mounting adapter thing I printed out. Now i can just make a .75" round recess in my actual knob and then I'll glue the adapter in place. The adapter is an extremely tight fit on the shaft right off of the machine - I had to do a bit of filing to make it fit snugly.