ASTM F959, Type A325 Direct Tension Indicator (DTI) washers are used to indicate the correct bolt tension when an A325 structural bolt is installed. The DTI is placed under a hardened surface such as a bolt head, nut, or hardened washer, with the bumps facing away from the structural steel. As the bolt is tensioned, the clamping force flattens the bumps, reducing the gap. The operator then checks the gap between the bumps to ensure the bumps have been crushed to within a determined tolerance, which results in the bolt reaching its proper tension. Dimensional specifications are governed by ASME B18.2.6. Available in mechanical galvanized finish, which provides a corrosion resistant zinc coating.