A bit holder has a shank at a proximal end thereof and a blind bit-accepting hole at a distal end thereof, shaped to receive a correspondingly-shaped tool bit. The bit holder has at least one locking mechanism comprising an opening defined in the bit holder, opening into a side of the bit-accepting hole. A locking element in the opening is moveable towards the opening to contact a tool bit in the bit-accepting hole. The bit holder has a sleeve around a body portion of the bit holder, overlying the opening and biased by a spring towards a normal position. The sleeve has an internal ramp angled to contact the locking element to urge the locking element towards the tool bit as the sleeve is moved into the normal position, and to accommodate the locking element when the sleeve is moved from the normal position against the force of the spring.