Picatinny rail
Another older, commercially available rail system is the Weaver rail, which was designed and popularized in the 1950s by William R. Weaver (1905-1975), and was the non-standardized conceptual precursor of the Picatinny rail. The main differences between the Picatinny rail and the Weaver rail are the rail dimensions and the spacing of the cross-slots, although the Picatinny rail is backward-compatible with almost all Weaver accessories (but not "vice versa").