embodiment the accessory body 30 defines a first stepped hole 301 for at least one end of the bit body 101 passing through along the pivot axis 101 a and includes a first restricting portion 31 arranged on the external surface of the accessory body 30 for fixing the stop member 40 and a second restricting portion 32 positioned in the first stepped hole 301 for preventing the bit body 101 moving apart from the function accessory 102 the function accessory 102 is preferably made of a transparent material the illustrated second restricting portion 32 further includes an annular plane 321 formed by the first stepped hole 301 and arranged substantially perpendicular to the pivot axis 101 a which is capable of preventing the first connecting portion 12 or the second connecting portion 22 from passing through the first stepped hole 301 the illustrated first restricting portion 31 includes a second annular protrusion 311 or a section of external thread arranged on the external surface of the accessory body 30 and the stop member 40 is a sleeve 401 which is mounted to the accessory body 30 by the second annular protrusion 311 or the section of external thread the stop member 40 includes a third annular protrusion 41 or section of internal thread arranged on an inner surface of the sleeve 401 the illustrated stop member 40 defines a through hole 42 which allows the working portion 11 or the driven portion 21 to pass.