the related art a locking state can be achieved at every 6 5 mm which is a half the distance of 13 mm between the locking pins 1 even though the locking pins 1 are alternately inserted in the locking holes 5 accordingly it is possible to make more locking states in the second form shown in fig5 a 5g the reference distance is 1 9 mm and when a locking pin 1 moves the reference distance to the right through total six steps it is inserted into the next locking hole 5 that is the first pin is inserted in a locking hole 5 in 0 step and when the locking pins 1 move the reference distance to the right into 1 step any locking pins 1 are not inserted in the locking holes 5 so a locking state is not achieved however when the locking pins move the reference distance into 2 step the fourth pin is inserted in a locking hole 5 further the third pin is inserted in a locking hole in 3 step a locking state is not achieved in 4 step and the second and the first pin are inserted in a locking hole 5 in 5 step and 6 step respectively which makes one cycle in this case a locking state is achieved at minimum every 1 9 mm.