A vehicle running board step construction and method of making and mounting the same on a hollow metal support pipe having a step portion and in turn adapted in vehicle-mounted orientation to extend generally adjacent a sill of a vehicle door. An upwardly facing exterior surface of the pipe step portion has an elongate mounting opening. The step construction includes a support plate having a plurality of transverse trusses arranged in spaced apart relation in a longitudinally extending row and adapted to straddle the pipe opening side edges and rest thereon for support. A plurality of spacer webs are individually interposed between and joined to longitudinally adjacent pairs of the trusses and support at each of their longitudinally opposite ends a resilient spring finger catch adapted to underlie an associated one of the pipe opening side edges. Each finger catch has a free end adapted to resiliently engage an interior surface of the pipe for holding the step plate against upward release from the pipe. The step construction also includes a step plate mounted on and covering the support plate, and adapted to also cover the mounting opening of the pipe. The step plate has a generally flat planar central step tread portion with an undersurface bearing upon the support plate trusses, and also has downwardly extending side flanges adapted to respectively extend outwardly of and downwardly past the pipe opening side edges and terminate at free end edges adapted to resiliently engage the exterior surface of the pipe. A plurality of retaining barbs extend downwardly from the step plate undersurface into snap lock tang engagement with associated receiving slot anchor tabs provided in the trusses for holding the step plate on the support plate, and vice versa.