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| ①,Material a、Faricated from alloy steel and shall conform in all respects to ASTM A574 b、Faricated from corrosion-resistant steel and shall conform in all respects to ASTM F837 ②,Heads may be plain or knurled at the option of the manufacturer, unless specified otherwise by the customer. For knurled screws, the maximum head diameter shall be measured across the tops of the knurl, and the minimum head diameter shall be the diameter of the unknurled portion or the diameter across the tops of the knurl for those screws not having an unknurled portion, just above the radius or chamfer at the bottom edge of the head . ③,Thread. Thread shall be Unified external thread with radius root: Class 3A UNRC and UNRF Series for screw sizes 0 (0.060 in) through 1in.; Class 2A UNRC and UNRF Series for sizes over 1 in. to 1-1/2 in., inclusive; and Class 2A UNR Series for sizes larger than 1-1/2 in. For plated or unplated screws, acccptability shall be based upon System 22, ASME B1.3. Class 3A does not provide a plating allowance. ④,Surface Roughness. For alloy steel screws of sizes up to and incuding 5/8 in., and nominal lengths equal to or less than 8 times the basic screw diameter, the surface roughness of the screws shall not exceed 63 μin. (arithmetical average) on the fillet and head bearing surfaces, nor exceed 32 μin. (arithmetical average) on the threads. For larger sizes, longer lengths, and corrosion-resistant steel screws, the surface roughness of the screws shall not exceed 125 μin. (arithmetical average) on the body [see Note (8)], fillet [see Note (14)], and head bearing surfaces. Normally, it shall be sufficient to ascertain that these surfaces on screws have the equivalent of a smooth machined finish by visual comparison with known surface standards. However, where it is practical and deemed necessary to measure these surfaces with commercially available equipment, roughness measurements shall be taken axially on the body and fillet surfaces, and circumferentially on the bearing surface. (See ASME B46.1, Surface Texture .) |
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