Machinery's Handbook, 31st Edition
Fasteners for Structural Applications 1705 Body length, L B , min., is the distance measured parallel to the axis of bolt from the under- head bearing surface to the last scratch of thread or to the top of the extrusion angle. It shall be used as a criterion for inspection. The minimum body length, as calculated and rounded to two decimal places, shall be equal to the maximum grip gaging length minus the maximum transi- tion thread length ( L B, min = L G, max − Y max ). Bolts of nominal lengths which have a calculated L B, min length equal to or shorter than 2.5 times the thread pitch for sizes 1 inch and smaller, and 3.5 times the thread pitch for sizes larger than 1 inch shall be threaded for full length. Transition thread length Y is a reference dimension, intended for calculation purposes only, which represents the length of incomplete threads and tolerance on grip gaging length. (11) Incomplete Thread Diameter : The major diameter of incomplete thread shall not ex - ceed the actual major diameter of the full form thread. (12) Threads : Threads, when rolled, shall be in the Unified inch coarse or 8 thread series (UNRC or 8 UNR Series), Class 2A. Threads produced by other methods may be Unified inch coarse or 8 thread series (UNC or 8 UN Series), Class 2A. Acceptability of screw threads shall be deter - mined based on System 21, ANSI/ASME B1.3, screw thread gaging systems for dimensional acceptability, unless otherwise specified. (13) Identification Symbols : Identification marking symbols on the tops of heads for bolt sizes 5 ∕ 8 inch and smaller shall project not less than 0.005 inch above the surface nor more than 0.015 inch over the specified maximum head height. Bolt sizes larger than 5 ∕ 8 inch shall project not less than the equivalent in inches of 0.0075 times the basic bolt diameter above the surface nor more than 0.030 inch over the specified maximum head height. (14) Material . Chemical and mechanical properties of steel bolts shall conform to ASTM A325 or ASTM A490. (15) Nominal Size . Where specifying nominal size in decimals, zeros preceding the decimal and in the fourth decimal place shall be omitted. (16) Dimensional Conformance . Heavy hex structural bolts shall have the following characteristics inspected to ANSI/ASME B18.18-2017 to the inspection level C: threads, width across comers, head height, grip length, visual. If verifiable in-process inspection is used, see Dimensional Characteristics on page 1705. Identification Source Symbols: Each bolt shall be marked to identify its source (manufacturer, or private label distributor) accepting the responsibility for confor - mance to this and other applicable specifications. Quality Assurance: Unless otherwise specified, products shall be furnished in accordance with ANSI/ASME B18.18-2017 as noted as below. Dimensional Characteristics: Bolts shall conform to the dimensions indicated in Table 5 . The designated characteristics defined in Table 5 , Note (16) shall be in - spected in accordance with ANSI/ASME B18.18. For nondesignated characteristics, the provisions 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. Heavy Hex Nuts.— Width Across Flats: The width across flats of heavy hex nuts shall be the overall distance measured, perpendicular to the axis of the nut, between two opposite sides of the nut in accordance with the notes of Table 6 . For milled-from-bar hex nuts, the nominal bar size used shall be the closest commercially available size to the specified basic width across flats of the nut.
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