A friend of mine has a Miata. It’s an automatic (don’t hate - he has a bad knee, and constant clutch use aggravated it). He knows I recently got a small wood lathe, and is interested in having me make him a new shift knob. I do have a scrap of walnut left over from the chair. I haven’t had a chance to look at the existing shift knob. Do they generally just screw on/off, and if so, is there a standard size? Is there anything else I should be aware of for making him a new one?