R8 3" Head Boring Tool Set ~ Rugged design allows excellent rigidity for chatter-free boring. ~ Head features a threaded back for use with multiple shanks. ~ Set complete with boring head, boring shank, carbide tipped boring bars & L-shape hex wrenches. ~ Dial on head with 0. 0005" graduation for accurate hole sizing. ~ Fitted durable carrying case included. ~ 12 boring bars. ~ Boring bar hole size is 3/4". ~ 1 DIV = 0. 001 which means on the 0-50 dial when turning the dial by 1 division/graduation, the boring head's travel is 0. 001" in radius movement and 0. 002" in diameter movement. On the 0-100 dial, the boring head's travel is 0. 0005" in radius movement, 0. 001" in diameter movement. ~ Boring head thread is 1~1/2"-18. ~ Offset is 3/4". ~ Cross hole is 3/4". ~ Shank thread is 7/16"-20. ~ Minimum bore diameter is 0. 394". ~ Maximum bore diameter is 7. 874". ~ Maximum bore depth is 3. 15".