I went through a lot of screw piloting drill bits before I settled on this combination. The tapered drill bit is sold by Lee Valley, and the countersink is by Dimar. This is THE best countersink that I have ever used. It uses carbide cutters that last and last and last. The whole unit is made in two parts that clamp around the drill bit. This allows the depth of cut to be easily adjusted and it allows for the cutter to bit used on many sizes of drill bits.