Machinery's Handbook, 31st Edition
Fasteners for Structural Applications 1707 (6) Width Across Flats : Maximum width across flats shall not be exceeded (see exception in Heavy Hex Nuts.—Width Across Flats ). No transverse section through the nut between 25 and 75 percent of the actual nut thickness, as measured from the bearing surface, shall be less than the minimum width across flats. For milled-from-bar nuts, Heavy Hex Nuts.—Width Across Flats , pertaining to the nominal bar size to be used. (7) Threads : Threads shall be UNC or 8 UN Class 2B in accordance with ANSI/ASME B1.1, Unified Inch Screw Threads. When specified, 8 thread series may be used on nuts over 1 inch in diameter. (8) Dimensional Conformance : Heavy hex nuts shall have the following characteristics inspected to ANSI/ASME B18.18-2017 to the inspection levels as follows: Width across corners, inspection level C; Thickness, inspection level B; Visual, inspection level C. If verifiable in-process inspection is used, see Dimensional Characteristics on page 1707. Nut Thickness: The nut thickness shall be the overall distance measured parallel to the axis of nut, from the top of the nut to the bearing surface, and shall include the thickness of the washer face where provided. Threads: Threads shall be in accordance with Table 6 , Note (7). Thread Gaging: Unless otherwise specified by the purchaser, gaging for screw thread dimensional acceptability shall be in accordance with Gaging System 21 as specified in ANSI/ASME B1.3 Screw Thread Gaging Systems for Acceptability: Inch and Metric Screw Threads (UN, UNR, UNJ, M, and MJ). Overtapping: When nuts are zinc coated, they shall be overtapped after coating in accor dance with the provisions of ASTM A563. Finish: Unless otherwise specified, nuts shall be supplied with a plain (as-processed) finish, unplated or uncoated. Materials: Chemical and mechanical properties of heavy hex nuts shall conform to ASTM A563. Workmanship: Nuts shall be free from burrs, seams, laps, loose scale, irregular surfaces, and any defects affecting their serviceability. When control of surface discontinuities is required, the purchaser shall specify conformance to ASTM F 812/F 812M, Surface Discontinuities of Nuts—Inch and Metric Series. Designation: Nuts shall be designated by the following data in sequence shown: product name, nominal size (fraction or decimal), threads per inch, material (including specifica tion where necessary), protective finish (if required). See example below: Example: Heavy Hex Nut, 1 ∕ 2 -13, ASTM A563 Grade C, Plain Finish Identification Grade Symbols: Each nut shall be marked in accordance with the require ments of the applicable specification: ASTM A563 or ASTM A194. Identification Source Symbols: Each nut shall be marked to identify its source (manufac turer, or private label distributor) accepting the responsibility for conformance to this and other applicable specifications. Quality Assurance: Unless otherwise specified, products shall be furnished in accor dance with ANSI/ASME B18.18 as noted in Dimensional Characteristics . Dimensional Characteristics: Products shall conform to the dimensions indicated for the heavy hex nut in Table 6 . The designated characteristics defined in Table 6, Note (8) shall be inspected in accordance with ANSI/ASME B18.18. For nondesignated characteristics, the provision of ANSI/ASME B18.18 shall apply. Should a nondesignated dimension be determined to have a variance, it shall be deemed conforming to this Standard if the user, who is the installer, accepts the variance based on fit, form, and function considerations. Where verifiable in-process inspection is used in accordance with ANSI/ASME B18.18-2017, the final inspection level sample sizes of those respective standards shall apply.
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