Collet System ER Collet Series ER20 Shank Type Taper Shank Taper Size BT30 Projection Decimal Inch 4 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