Indexable Boring Tool Set with 3 in. Boring Head, R8 Shank & 8 Boring Bars Boring head features a 1-1/2 in.-18 threaded back so you can change shanks as needed. A micrometer lead screw provides 0.001 in. direct reading accuracy and makes adjusting easy. Boring head offset is 1 in.. Minimum boring diameter is 0.394 in.. Maximum boring diameter is 7.874 in.. Maximum boring depth is 3.150 in.. The crosshole is 3/4 in.. R8 shank has a drawbar end thread of 7/16 in.-20. The included indexable boring bars come with TCMT 21.5 C6 carbide inserts for steel and alloy. The set also comes with torx & l-shape hex wrenches and a fitted carrying case. A micrometer lead screw provides 0.001 in. direct reading accuracy and makes adjusting easy. 1 DIV = 0.001 which means when turning the dial by 1 division/graduation, on the 0-100 dial, the boring head’s travel is 0.0005 in. in radius movement, 0.001 in. in diameter movement.