ASTM F959 / F959M DTI Washers

ASTM F959/F959M DTI washers are compressible-washer-type Direct Tension Indicators used with structural fasteners to indicate the achievement of a specified minimum bolt tension. The product is commonly known as a DTI washer or Direct Tension Indicator and is used as part of structural bolting assemblies rather than as a conventional flat washer. ASTM F959/F959M covers both inch and metric series.

The specification covers DTI types associated with structural bolt assemblies, including Type 325, 325-3, 490, 490-3, 8.8-1, 8.8-3, 10.9-1, and 10.9-3. The current standard covers nominal diameters from 1/2 to 1-1/2 in. and M16 to M36. Inch-pound and SI dimensions are treated as separate systems under the specification, so the required dimensional system should be identified when specifying or purchasing the product.

ASTM F959/F959M DTI washers are used in structural steel connections where controlled bolt tension is important, including steel buildings, bridges, infrastructure, industrial structures, and heavy structural assemblies. They are intended for installation with the indicator protrusions against a hardened surface such as a bolt head, hardened nut, or hardened washer.