The bit-handle is designed to hold standard-bits (Bosch, Makita etc.). The bit is hold in place by a magnet (10x3 mm). It e.g. helps driving screws in tight areas or just to carry tools around if space is limited. I supply the handle with a special bit to allow friends mounting some of my creation I deliver to them in parts, The thread of the insert is slightly undersized to allow a good fit.