• Tri-flat shank design for sure grip in chuck without slippage Set Includes: • 1/4" Shank: 3/16" to 1/2" holes in 1/16" steps • 1/4" Shank: 1/8" to 1/2" holes in 1/32" steps • 3/8" Shank: 1/4" to 3/4" holes in 1/16" steps • 3/8" Shank: 3/16" to 7/8" holes in 1/16" steps • 3/8" Shank: 1/4" to 1-3/8" holes in 1/8" steps