Sherline manufactures its own 3/8" diameter boring bars as P/N 2259 (80°) and P/N 2260 (55°). They are also available as a set as P/N 2261 at a substantial cost savings. Each Sherline tool holder comes with an insert, hold-down screw and Torx tool. The boring bars are 3.25" long and will bore a hole up to about 2" deep. The 80° holder requires about a 1/2" hole size minimum, while the 55° holder requires a hole of 3/4" to get started. 2261 Sherline Pairing Boring Tools Instructions