Don't most aftermarket shift knobs come w/ adapters for different thds? What type of material is on the inside of your knob? Plastic or metal?
If it's plastic, then you and probably xthread it on to your shifter ONCE, but I'd probably put some thread lock or something on there to help it keep.
If it's metal, and you REALLY want the knob, you'll either have to find a plastic sleeve that will make up the difference between the current shifter (hopfully smaller and your knob diameter) and thread it on. If the hole in the knob is smaller than the shifter stick, then you'll have to take it to a shop or stick it in a vice and drill it out and re-tap it to match.
I'd look for some sort of thread adapter, I know they are out there.