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| ③,7#, 14#, 16#, 18#, 20#, 24# are for tapping screws only. ④,9/16, 5/8, 3/4 are for machine screws only. ⑤,The diameter of body on machine screws having other than trim heads shall not be less than the Class 2A thread minimum pitch diameter nor greater than the basic major diameter of the thread. ⑥,Machine Screw Length of Thread 1) Sizes No.5 and smaller. Screws of nominal lengths equal to three diameters and shorter shall have full-form threads extending to within one pitch (thread) of the bearing surface of the head, or closer, if practicable. Nominal lengths greater than three diameters, up to and including 1-1/8 in., shall have full-form threads extending to within two pitches (threads) of the bearing surface of the head, or closer, if practicable. Screws of longer nominal lengths shall, unless otherwise specified, have a minimum length of full-form thread of 1 in. 2) Sizes No.6 and smaller. Screws of nominal lengths equal to three diameters and shorter shall have full-form threads extending to within one pitch (thread) of the bearing surface of the head, or closer, if practicable. Nominal lengths greater than three diameters, up to and including 2 in., shall have full-form threads extending to within two pitches (threads) of the bearing surface of the head, or closer, if practicable. Screws of longer nominal lengths shall have a minimum length of full-form thread of 1.5 in. unless otherwise specified. ⑦,Machine Screw Material 1)non-heat-treated low carbon steel, such as1006 through 1038 2)When hardened machine screw are specified, they shall be made from low or medium carbon steel, such as 1018 through 1038, with or without boron, through-hardened to Rockwell C25-38 |
