CASTLE NUT FASTENING DEVICE

PURPOSE:To ensure the insertion of a cotter pin by irradiating light from the radial outside of a socket to the center axis of the latter, and by detecting, by use of a light receiving sensor, whether a groove in a castle nut aligns with a through hole in a bolt or not. CONSTITUTION:A castle nut 1 is fitted in a recess 15 in the forward end of a socket 13, and an outer cylinder 17 is set in such a direction that a light beam between light emitting and receiving sensors 23, 27 aligns with a through- hole 5 in a bolt 4. Further, the socket 3 attached to a spindle anvil 11 is rotated together with the nut 1 which is therefore screwed onto a bolt 4. Therefore, irradiation holes 20, 21, a small hole 16 and a groove 3 in the nut 1 temporarily align with each other, but a light beam does not reach the light receiving sensor 27 since the groove 3 and the through-hole 5 are shifted axially from each other. When the nut is fastened to a present value, an impact wrench is automatically stopped, but is restarted if the groove 3 does not align with the through- hole 5 while is is stopped if they align with each other. Thus, it is possible to prevent the attachment of a cotter pin from being missed.