It allows a user to secure drill bits from 3/16" up to 3/4", holding jaws tightly into place for reduced bit slippage. If your drill's bit retention is suffering, the rotation feels stiff, or the chuck has seized up entirely, a new chuck should fix the problem. Please note this purchase includes a durable heavy -duty chuck(48-66-2085), chuck key(48-66-3160) and key retainer(48-66-4020).