Abstract: A blow-molded plastic structure may include an inwardly extending portion with an undercut. The inwardly extending portion may be disposed in an outer surface of the blow-molded plastic structure and the undercut may be disposed in the inwardly extending portion. The structure may be formed by placing a tool in a mold, forming a parison of molten plastic, disposing the parison of molten plastic in the mold, closing the mold around the parison of molten plastic, inflating the parison, and creating an inwardly extending portion with an undercut with the tool during the blow-molding process. The tool used to create the undercut in a blow-molded plastic structure may include a base, one or more guides, and one or more fingers movable relative to the base between a molding position and a release position. The fingers may include an elongated body and an outwardly extending portion.

Abstract: A large, thin, generally planar panel constructed from blow-molded plastic may include a first surface, a second surface, and a hollow interior portion disposed between the first and second surfaces. The panel may include a nominal panel thickness (PT), which may be the distance between the first surface and the second surface, and a nominal wall thickness (WT), which may be the thickness of the outer wall of the blow-molded plastic structure. A plurality of depressions may be integrally formed in the second surface and a nominal distance (D) separating adjacent depressions may be measured from an edge of one depression to an edge of the adjacent depression. The relationship between the nominal panel thickness, the nominal wall thickness, and the nominal distance between adjacent depressions is shown by the equation WT·PT·D?0.030.