Collet System ER Collet Series ER20 Shank Type Taper Shank Taper Size BT30 Projection Decimal Inch 25 DIN Coolant option standard All Ground Body Factory Balanced to save spindle life, tool life and increased productivity Threaded through holes for a backup screw tool stop or coolant through when removed Wrench not included BT30BT40 Premium balanced to 30,000 rpm BT50 Premium balanced to 25,000 rpm