I have a geared DC motor taken from a hand drill. When I manually turn the internal motor, the drill bit rotates. This can be done in both directions. However If I try and turn the drill bit it does not rotate. What is the mechanism called that achieves this? My friend says it is a sprag clutch. But from what I have read a sprag clutch is used to only allow either clockwise or anticlockwise rotation, which is not what's happening here. But is he correct?