ASME B18.21.1 is the definitive American standard for Inch Series Washers, specifically focusing on locking mechanisms and general-purpose flat washers. It provides the dimensional and mechanical requirements for fasteners intended to maintain tension and prevent the unintentional loosening of bolted joints in North American industrial applications.

The standard covers a broad spectrum of hardware, including Helical Spring Lock Washers (Standard, Heavy, and Hi-Collar), Tooth Lock Washers (Internal and External), and Plain Washers. This diversity allows engineers to select the specific locking characteristic required for varying vibration and load environments.

The technical advantage of ASME B18.21.1 locking washers lies in dynamic tension maintenance. Helical washers act like a spring, providing a constant axial force that increases friction between the threads. Tooth washers, conversely, utilize physical "bite" to dig into the bearing surface and the bolt head, creating a mechanical barrier against rotation. Selecting the correct type depends on the surface hardness of the joined materials and the severity of expected vibrations.