Preload indicating (PLI) washers are said to provide accurate measuring of the clamp force in a bolted joint, and work with joints that are inaccessible to torque wrenches.
Standard PLI washers are suitable for use under locknuts to induce an average preload of 80% of the yield strengths in bolts ranging from 80 to 260-ksi minimum ultimate tensile strength. Washer types include standard for use under the nut, under the head for small spaces, and oversize for use with reworked joints. Sizes range from #10 to 11/2 diameters in alloy steel, cadmium plated to QQ-P-416, and corrosion-resistant A286 material.
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