1) Men-an-tol, Tolven and Long stones are considered healing stones; healing attributes were usually associated with stones with holes.

2) Widdershins means counterclockwise, or in the case of ancient rituals it refers to the direction against the sun, i.e. where you are unable to see your shadow. At Men-an-Tol a neck crick would be cured after passing 3 or 9 times through the hole, usually against the sun. To ensure a cure at the Tolvan stone, you must sleep with a sixpence under your head on the grassy mound by the stone after the passing ritual is complete. Folklore has the Long Stone running around the field when the nearby Minchinhampton town clock strikes midnight.

3) Healing rituals required a specific number of passages through the hole - 3 or 9 times depending on which stone.

Source of info: http://witcombe.sbc.edu/earthmysteries/EMHealing.html