I'm looking for a couple of tone knobs for my '78 Ludwig Vistalite snare and 18" floor tom. I've looked on ebay but all the ones for sale there have only one screw to attach it to the drum. The knobs on my other drums have three screws. I need two knobs that have three screws. Any info on where I can find these would be great. Also why can't i find any examples of the three screw ton knobs?

thanks

derek