as to project through these slots when the covers are closed push buttons 97 also project from the front of plate 91 one from each vertical half of the plate latch member 90 may be inserted into latch pocket recess 69 in the manner shown in fig7 and 8 initially the latch 90 is tilted relative to recess 69 with its top forward or its bottom forward if it is desired to insert the latch bottom first the bottom guide member 94 is then brought up into recess 69 as shown in fig7 the latch member is moved upward until both members 92 are above and beyond divider 75 whereupon the top of the latch member is rotated back toward the recess the bottom of the latch member being constrained in the recess by lips 74 76 acting on bottom guide member 94 upon continued rotation of the latch member the forward edge 70 of divider 75 abuts the back side of plate 91 at a location below the members 92 the constraints at bottom guide member 94 and edge 70 as seen in fig8 result in flexure of the plate 91 upon continued rotation of the latch this permits the upper guide member 94 to be pushed behind the plane of lips 74 76 from which position the latch 90 is pushed down until the upper and lower guide members 94 are both inside recess 69 and constrained by lips 74 76 this downward push which might otherwise be impeded by divider 75 blocking lower member 92 is facilitated by a sloped guide member 98 which rides along edge 70 of the guide member during insertion.