projection 42 are located at the same angular position eight recesses 43 are provided on the bottom surface of the plate 9 at equally spaced intervals eight recesses 44 are provided on the upper surface of the cover 6 at equally spaced intervals in the state shown in fig3 and 35 each recess 43 of the plate 9 is displaced from each recess 44 of the cover 6 by 2 u03c0 16 radians in the circumferential direction the bobbin 8 and the shifter 40 are slidable along an axis 7a and urged upward by a compression coil spring 20 supported by the cover 6 as shown in fig3 34 and 35 the top projections 41 of the shifter 40 are received by the recesses 43 of the plate 9 and the bottom projections 42 of the shifter 40 are separated the corresponding recesses 44 of the cover 6 by the action of the spring 20 respectively fig3 37 and 38 show the state in which the bobbin 8 and the shifter 40 move downward against the action of the spring 20 in this case the bottom projections 42 are received by the cover recesses 44 and the top projections 41 are spaced from the plate recesses 43 as shown in fig3 when a short pin 24 is inserted into only a bore 22 of.