that the upper end of the pole piece assumes a northerly magnetization selector card 11 will be pivoted as illustrated if the bar magnet 24 has its left end of a north polarity the selector card 11 includes a pair of notches 34 and 35 which upon rotation and downward movement of the card will engage either projection 20 as shown or a corresponding projection on the other side that is not shown to operate either one of the latch arms 16 or 17 upon de energization of the coil the selector card will be pulled upward during this movement projections 36 and 37 will engage the projections such as pin 20 to return the latches to their normal position it can readily be seen from the above description of the environment of the selector card that its dimensions and overall size are very critical and that therefore the arrangememnt for retaining the polarizing magnet on the card is constrained looking at fig2 it can be seen that the card is of a generally deltoid shape with three projections from the upper end a central tongue like projection 40 having formed therein a saddle like depression 41 with a section view at 2a for confining the magnet on the back side 42 the bottom side 43 and on the top at 44 the two other projections 45 and 46 one on each side of the central projection serve to resiliently position the magnet when it is placed in the central saddle axially between themselves and against the back portion 42 this latter action is performed by the projections such as.