Loose knob fix tip, cheap and super easy!

I don't like my knobs too loose but they get that way over time, well before they need replacing. So what I do is take the knob off, cut a short piece of shrink tube 1/4" or 5/16", whatever slips over and covers about half of the spline/shaft height wise but doesn't fit too sloppy around the spline. Then, press the knob back down and tighten set screw. If the action is too loose cut another piece of longer tube or too tight, trim off a little. No harm is done because both friction surfaces are metal (tele) or hard plastic (strats) and the "bearing" is soft plastic. Also, because the "bearing" is sort of a tight fit around the spline, it wont deform and mar the paint underneath on rear control cavity tele's, like mine.

I guess you could use a straw from McDonalds or something similar but the stiffer the material, the more precise your length has to be because the compression you add to stiff materails really adds up fast to making the nob turn harder. That is why I like shrink tube in its raw form, soft and durable!