Abstract: A snap-on drop away register guide for use with a Heidelberg platen in a Heidelberg printing press includes a reciprocating spring biased plunger having transversely mounted thereon, for oscillating movement, a retractable guide plate. A camming arrangement exists between the guide plate and plunger which is operable upon rectilinear movement of the latter to effectuate the oscillating movement of the former between extended and retracted positions. A one-piece, snap-on raiser quickly changes the height of the lower paper margin and is provided with a vertical rib on one of two depending legs which cooperates with an offset on the drop away register guide to prevent improper mounting of the raiser on the drop away guide. An extension side guide for the Heidelberg platen includes an adjustment device for the lock screw thereof which not only permits the side guide to remain on the platen when not in use but also sideways movement relative to the platen.