as shown in fig2 each of the first legs 32 1 is located outside the first projection 41 of each locking pin 40 and each of the second legs 32 2 is located within the space 44 defined between the first projection 41 and the second projection 42 in one embodiment the legs 32 support the locking pins 40 and simultaneously allow the locking pins 40 to move in the leftward and rightward horizontal directions in one embodiment locking pins 40 may be provided with a first projection 41 formed between the first and second legs 32 1 and 32 2 and a second projection 42 formed apart from the first projection 41 at a predetermined interval in order to define a space 44 in which the second leg 32 2 is received locking pins 40 are preferably fixed so as not to escape from the legs 32 in this and other embodiments if any of the locking pins is not positioned to be inserted into through holes in track 1 first legs 32 1 and or second legs 32 2 press against first projection 41 and or second projection 42 respectively to prevent any of the locking pins from inserting into through holes in track 1 accordingly all locking pins 40 must be aligned with a through hole to lock the pins to track 1 this ensures that the strength of all locking pins contribute to holding the seat in the track in the event of a collision as will be recognized although the number of.