Tony, here is what I use. It's a .375 counterbore with a .25 pilot. There are hobby items around but they are not that good for this purpose. I got mine at a tool store that supplies machine shops. Try these guys if you can't find some thing like I have around where you live. Don't settle for something less. It is too important. Dan
http://www.mcmaster.com/#counterbores/=h1rc2d