ASTM F959 Round Structural Washers are compressible washer-type direct tension indicators, in nominal diameter sizes 1/2 through 1-1/2 in. Often referred to as DTI’s, these bolt load cell washers are designed, when installed as directed, to indicate the achievement of a specified minimum bolt tension in a F3125 series structural bolt assembly. During assembly the DTI washer protrusions should always face towards the underside of the bolt head or nut face. Washer protrusions should NOT be placed against the surface of the materials being bolted together. DTI's are individual bolt load cells, which measure pretension developed during tightening, regardless of torque resistance of the bolt. DTI’s are installed on only one end of a bolt assembly and tightened until the protrusions, (bumps), are compressed enough so that a feeler gage cannot be inserted into the gaps between protrusions. ASTM F959 Washers are available in both a plain finish and in a mechanically galvanized coating for superior corrosion resistance where required.