So I lost the middle knob on my '92 American Fender Jazz Bass and I went to the shop to get a new one. Now the knob they gave me looked ok but when I tried putting it on it didn't fit and I noticed that it didn't have a small screw like the other knobs did. My questions is: what kind of knobs do I need and do they still exist (the bass is 16 years old after all).

Thanks guys
Oh. Even if they are, I'm not exactly sure how that helps your situation. lol

But finding knobs shouldn't be TOO hard, and if not, replace the whole set maybe? But if you don't want to, just find a knob with the right size hex hole.
just buy a replacement knob on ebay, es what i did for fender knobs for my squier. worked perfectly (except the fact i stripped the knobs)
Try adding more delay.