Self-tightening key-less feature automatically increasing gripping force, high reliability, and stability. Special quenching treated key parts increases durability. Suitable for drill presses or lathes spindle accepts MT3 Arbor. VERY IMPORTANT: BEFORE YOU MAKING THE PURCHASE, PLEASE MAKE SURE YOUR DRILL PRESS/MILLING MACHINE TAKES THE MT3 (MORSE TAPER 3) SHANK. THE ARBOR IS MT3 NOT MT2 (THE MT3 ARBOR AT LARGE END IS 0.94")