the front face 44 receives the latch pin 54 which retains the sliding latch member 36 in the closed position the sliding latch member 36 has rivets 56 58 which extend through their respective slots 48 52 the rivets 56 58 have heads 60 which are wider than the slots 48 52 in order to retain the sliding latch member 36 on the right upright 24 the rivets 56 58 are positioned so that they bottom out and top out in their respective slots at the same time there is a spring 62 which is mounted at its upper end to the rivet 56 and at its lower end to the right upright member 24 in order to open the latch the sliding latch member 36 must be lifted up against gravity and against the force of the spring 62 and when the sliding latch member 36 is released the spring and gravity cause the sliding latch 36 to slide downwardly to close the latch the latch pin 54 is mounted on the sliding latch member 36 opposite a hole 64 in the front face of the sliding latch member 36 a spring 66 urges the latch pin 54 to extend through the hole 64 when the sliding latch member 36 is.