A fastening system for panels and trim having a fastening element including a reveal edge and a serpentine edge. A projection and a recess is disposed adjacent to each other on the same serpentine edge. The fastening element guides and connects adjacent panel faces into a flush horizontal alignment with each other. Panels with the fastening element on each side may be combined together in a multiple course structure. The fastening element accommodates dimensional changes in adjacent wood panels from moisture and temperature fluctuations by allowing for expansion both with the elimination of the gap in the serpentine edge expansion area and with the compression of the expansion relief aperture adjacent to the expansion bulge in the recess of the adjacent panel. An expansion relief aperture on the projection of a fastening element can receive a trim fastener for applying perimeter trim with a hidden fastener onto many structurally different panel designs.