Although many older hand-cranked drills survive - and are still used - the great majority have one serious drawback, a single, rather low speed. In the case of the 2-speed Mancuna this limitation was overcome by the use of two concentric crown wheels, one small, the other large, each able to be engaged with its own pinion, these being positioned one above the other - the higher of the pair able to be lifted up and down and locked to the lower by dogs on their facing surfaces.  A form of automatic mechanical down-feed was fitted, a ratchet being indexed round by the action of a lever activated by a cam formed on the inner side of the handwheel shaft.