An extrusion device for mounting a wall panel has an outer cap extending to an edge on at least one side which is positioned against an outer surface of a wall panel, having a pair of spaced-apart insertion fingers, and a receiver base having a planar mounting portion and a pair of angled receiver flanges projecting upwardly to receive the insertion fingers therein. The two-piece extrusion permits wall panels to be mounted or removed from the underlying wall structure in on-sequential order. The receiver base and cap can be provided on both sides to form an "H" type extrusion, or on only one side in a "J" type extrusion. Preferably, the outer cap is made of metal, and the tips of the insertion fingers are beveled at a slight angle of about 7° to 14° to allow easy insertion into the receiver flanges. The cap has compound water-shedding edges formed with a rounded rain-drip edge spaced in close proximity to a sharply inclined knife edge. In another variation, a one-piece extrusion device has a rear base portion and a front cover portion forming a pocket therewith, and a ramp formed on the base portion within the width of the front cover portion for gradually forcing the edge of a wall panel inserted in the pocket toward the front cover portion clear of the heads of screws used to mount the base portion to the underlying wall structure. The base portion is formed with a hook indentation on a back side of the ramp on a rear surface of the base portion, and interconnects with a "Z" type extrusion having a hook end to form a right angle connection. The one-piece extrusion may be formed as a "J" (one-sided), "H" (two sided), "C" (corner), or other suitable types.