HHIP 6 Piece High Speed Steel 3 Flute Solid Pilot Counter bore Set includes one each of 1/4, 5/16, 3/8, 1/2, 5/8, and 3/4". It is made of high speed steel. 3-flute, straight shank. Supplied with fitted wooden case. Continuous pilot counter bores cut rapidly, smoothly and accurately producing long spiraling chips rather than small metal particles. 1/4" counter bore has a 9/32" pilot diameter, a 13/32" cutter diameter, a 5/16" shank and is 5" long. 5/16" counter bore has a 11/32" pilot diameter, a 1/2" cutter diameter, a 3/8" shank and is 5" long. 3/8" counter bore has a 13/32" pilot diameter, a 19/32" cutter diameter, a 1/2" shank and is 6" long. 1/2" counter bore has a 17/32" pilot diameter, a 25/32" cutter diameter, a 1/2" shank and is 7-1/2" long. 5/8" counter bore has a 21/32" pilot diameter, a 31/32" cutter diameter, a 5/8" shank and is 7-1/2" long. 3/4" counter bore has a 13/16" pilot diameter, a 1-3/16" cutter diameter, a 3/4" shank and is 8" long.