1. Self-tightening feature automatically increases gripping power. Special design & manufacture against for super heavy torque(clamping capacity)use.2. Owing to inspecting strictly & with excellent RUN-OUT Accuracy and quality guaranteed the gripping power is double than general brand. Especially suitable for CNC machining center & milling machining use.3. Avoid the drill dropped when used in instance change of direction and equipped with spanner for tightening perfect safety.