This ‘OT’ Receiver has a slanted surface upon which the Latch hook slides when locking, imparting a lateral force that compresses the door against the case. This is especially beneficial when gasketing is involved. The ‘OT’ Receiver can be used either inside or outside a case. See TDSs 21-1, 21-2, 41-1 and 41-2.
Of particular interest the OTR187-2 has keyhole-shaped screw holes for the easy removal of these Receivers when used, for example, as window hardware for hurricane shutters. See TDS 207-2A1.