platen 49 also includes a rectangular flange or neck 50 extending forward from its front face symmetrically disposed about the longitudinal center line of the secondary register platen as may be seen best by referring to fig1 and 1a the secondary register platen 49 has two notches 51 cut forward from its rear face 52 the notches 51 have arcuate inner faces and are coaxially aligned with the upwardly protruding studs 39 of the primary register platen 36 when the secondary register platen 49 is in congruent parallel alignment with the primary register platen the secondary register platen 49 also includes a hole 53 through its thickness dimension near the front face 54 of the secondary register platen the hole 53 is coaxially aligned with the upward protruding stud 42 of the primary register platen 36 when the secondary register platen is in congruent parallel alignment with the primary register platen with a secondary register platen 49 thus aligned with and overlying the primary register platen 36 the notches 51 of the secondary register platen may be engaged with the studs 39 of the primary register platen and the neck 50 of the secondary register platen pivoted downwards into parallel alignment with the neck 37 of the primary register platen until the stud 42 near the front face of the neck of primary register platen engages the hole 53 near the front face of the neck of the secondary register platen in this way a secondary register platen 49 may.