Bench Drilling: T38 (1Â 1/2") Guide tube: for bit dia. 67-76mm. D56mm,L950mm,1220mm,1525mm,1830mm,3050mm,3660mm; T45(1 3/4") Guide tube: for bit dia.76-89mm,and 89-102mm. D63mm/D76mm,L3050mm,3660mm; T51(2") Guide tube: for bit dia.89-102mm, and 102-127mm.D76mm/D87mm,L3050mm,3660mm.