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    2. B18.2.1 Heavy Hex Bolts

    ASME B18.2.1 Heavy Hex Bolts – Dimensions, Specifications & Standards

    Heavy Hex Bolts – Wide Head Profile for Critical Bolting Applications.

    ASME B18.2.1 Heavy Hex Bolts are robust inch-series fasteners featuring a larger hexagonal head than standard hex bolts, providing greater bearing area and superior resistance to loosening under high load and vibration — preferred for heavy structural, pressure vessel, and pipeline flange assemblies. The standard covers nominal sizes from 1/4 inch to 4 inches, including body diameter, width across flats, width across corners, head height, radius of fillet, and thread length. These bolts are manufactured per ASTM A1014/A1014M for UNS N07718 bolting with outstanding tensile strength, fatigue resistance, and corrosion resistance for extreme-temperature and high-pressure environments. Also furnished in ASTM A307 Grade B for structural bolting and ASTM A193 for pressure equipment service. Both ASME B18.2.1 for dimensions and the relevant ASTM specification for material performance must be referenced.

    HEAVY HEXAGON BOLT INCH THREAD

    ASME B18.2.1 Heavy Hex Bolts Dimensions (mm)

    Nominal Size or Basic Product Diameter Full-Size Body Diameter, E Width Across Flats, F Width Across Corners, G Head Height, H Radius of Fillet, R Nominal Thread Length, LT
    Max. Min. Basic Max. Min. Max. Min. Basic Max. Min. Max. Min. 152.4mm and Shorter Over 152.4mm
    3/8 9.525 9.855 9.144 17.463 17.475 16.993 20.168 19.380 6.350 6.807 5.740 0.762 0.254 25.400 31.750
    1/2 12.700 13.081 12.243 22.225 22.225 21.590 25.654 24.613 8.731 9.246 7.671 0.762 0.254 31.750 38.100
    5/8 15.875 16.307 15.367 26.988 26.975 26.187 31.166 29.845 10.716 11.278 9.601 1.524 0.508 38.100 44.450
    3/4 19.050 19.507 18.517 31.750 31.750 30.785 36.652 35.128 12.700 13.310 11.557 1.524 0.508 44.450 50.800
    7/8 22.225 22.733 21.641 36.513 36.525 35.408 42.164 40.361 14.684 15.342 13.487 1.524 0.508 50.800 57.150
    1 25.400 25.959 24.790 41.275 41.275 40.005 47.650 45.618 17.066 17.780 15.011 2.286 0.762 57.150 63.500
    1 1/8 28.575 29.185 27.889 46.038 46.025 44.602 53.162 50.851 19.050 19.812 16.713 2.286 0.762 63.500 69.850
    1 1/4 31.750 32.436 31.064 50.800 50.800 49.225 58.649 56.109 21.431 22.250 19.025 2.286 0.762 69.850 76.200
    1 3/8 34.925 35.662 34.163 55.563 55.575 53.823 64.160 61.366 23.019 23.876 20.574 2.286 0.762 76.200 82.550
    1 1/2 38.100 38.887 37.338 60.325 60.325 58.420 69.647 66.599 25.400 26.314 22.911 2.286 0.762 82.550 88.900
    1 5/8 41.275 42.113 40.411 65.088 65.075 63.017 75.159 71.857 27.781 28.346 24.841 2.286 0.762 88.900 95.250
    1 3/4 44.450 45.339 43.586 69.850 69.850 67.615 80.645 77.089 29.369 30.378 26.772 3.048 1.016 95.250 101.600
    1 7/8 47.625 48.565 46.711 74.613 74.625 72.238 86.157 82.347 31.750 32.410 28.702 3.048 1.016 101.600 107.950
    2 50.800 51.791 49.886 79.375 79.375 76.835 91.643 87.605 34.131 35.255 29.845 3.048 1.016 107.950 114.300
    2 1/4 57.150 58.547 56.236 88.900 88.900 86.055 102.641 98.095 38.100 39.319 33.706 4.826 1.524 120.650 127.000
    2 1/2 63.500 64.999 62.509 98.425 98.425 95.250 113.640 108.585 42.069 43.383 37.567 4.826 1.524 133.350 139.700
    2 3/4 69.850 71.806 68.859 107.950 107.950 104.445 124.638 119.075 46.038 47.473 41.453 4.826 1.524 146.050 152.400
    3 76.200 78.257 75.209 117.475 117.475 113.665 135.636 129.591 50.800 52.324 46.101 4.826 1.524 158.750 165.100

    ASME B18.2.1 Heavy Hex Bolts Length Tolerance (mm)

    Nominal Length Nominal Size (inches)
    1/4 to 3/8 7/16 and 1/2 9/16 to 3/4 7/8 and 1 1 1/8 to 1 1/2 Over 1 1/2
    Up to 25.4 mm, incl. +0.508
    0.762    		 +0.508
    0.762    		 +0.508
    0.762    		 ... ... ...
    Over 25.4 mm to 63.5 mm, incl. +0.508
    1.016    		 +1.016
    1.524    		 +1.524
    2.032    		 +2.032
    2.54    		 +3.048
    3.048    		 +4.572
    4.572
    Over 63.5 mm to 101.6 mm, incl. +1.016
    1.524    		 +1.524
    2.032    		 +2.032
    2.54    		 +2.54
    3.556    		 +4.064
    4.064    		 +5.08
    5.08
    Over 101.6 mm to 152.4 mm, incl. +1.524
    2.54    		 +2.032
    2.54    		 +2.54
    2.54    		 +3.048
    4.064    		 +4.572
    4.572    		 +5.588
    5.588
    Longer than 152.4 mm +2.54
    4.572    		 +3.048
    4.572    		 +3.556
    4.572    		 +4.064
    5.08    		 +5.588
    5.588    		 +6.096
    6.096

    ASME B18.2.1 Heavy Hex Bolts Dimensions (Inch)

    Nominal Size or Basic Product Diameter Full-Size Body Diameter, E Width Across Flats, F Width Across Corners, G Head Height, H Radius of Fillet, R Nominal Thread Length for Bolt Lengths, LT
    Max. Min. Basic Max. Min. Max. Min. Basic Max. Min. Max. Min. 6 in. and Shorter Over 6 in.
    3/8 0.3750 0.388 0.360 11/16 0.688 0.669 0.794 0.763 1/4 0.268 0.226 0.03 0.01 1.000 1.250
    1/2 0.5000 0.515 0.482 7/8 0.875 0.850 1.010 0.969 11/32 0.364 0.302 0.03 0.01 1.250 1.500
    5/8 0.6250 0.642 0.605 1 1/16 1.062 1.031 1.227 1.175 27/64 0.444 0.378 0.06 0.02 1.500 1.750
    3/4 0.7500 0.768 0.729 1 1/4 1.250 1.212 1.443 1.383 1/2 0.524 0.455 0.06 0.02 1.750 2.000
    7/8 0.8750 0.895 0.852 1 7/16 1.438 1.394 1.660 1.589 37/64 0.604 0.531 0.06 0.02 2.000 2.250
    1 1.0000 1.022 0.976 1 5/8 1.625 1.575 1.876 1.796 43/64 0.700 0.591 0.09 0.03 2.250 2.500
    1 1/8 1.1250 1.149 1.098 1 13/16 1.812 1.756 2.093 2.002 3/4 0.780 0.658 0.09 0.03 2.500 2.750
    1 1/4 1.2500 1.277 1.223 2 2.000 1.938 2.309 2.209 27/32 0.876 0.749 0.09 0.03 2.750 3.000
    1 3/8 1.3750 1.404 1.345 2 3/16 2.188 2.119 2.526 2.416 29/32 0.940 0.810 0.09 0.03 3.000 3.250
    1 1/2 1.5000 1.531 1.470 2 3/8 2.375 2.300 2.742 2.622 1 1.036 0.902 0.09 0.03 3.250 3.500
    1 5/8 1.6250 1.658 1.591 2 9/16 2.562 2.481 2.959 2.829 1 3/32 1.116 0.978 0.09 0.03 3.500 3.750
    1 3/4 1.7500 1.785 1.716 2 3/4 2.750 2.662 3.175 3.035 1 5/32 1.196 1.054 0.12 0.04 3.750 4.000
    1 7/8 1.8750 1.912 1.839 2 15/16 2.938 2.844 3.392 3.242 1 1/4 1.276 1.130 0.12 0.04 4.000 4.250
    2 2.0000 2.039 1.964 3 1/8 3.125 3.025 3.608 3.449 1 11/32 1.388 1.175 0.12 0.04 4.250 4.500
    2 1/4 2.2500 2.305 2.214 3 1/2 3.500 3.388 4.041 3.862 1 1/2 1.548 1.327 0.19 0.06 4.750 5.000
    2 1/2 2.5000 2.559 2.461 3 7/8 3.875 3.750 4.474 4.275 1 21/32 1.708 1.479 0.19 0.06 5.250 5.500
    2 3/4 2.7500 2.827 2.711 4 1/4 4.250 4.112 4.907 4.688 1 13/16 1.869 1.632 0.19 0.06 5.750 6.000
    3 3.0000 3.081 2.961 4 5/8 4.625 4.475 5.340 5.102 2 2.060 1.815 0.19 0.06 6.250 6.500

    ASME B18.2.1 Heavy Hex Bolts Length Length Tolerance (Inch)

    Nominal Length Nominal Size
    1/4 to 3/8 7/16 and 1/2 9/16 to 3/4 7/8 and 1 1 1/8 to 1 1/2 Over 1 1/2
    Up to 1 in., incl. +0.02
    0.03    		 +0.02
    0.03    		 +0.02
    0.03    		 ... ... ...
    Over 1 in. to 2 1/2 in., incl. +0.02
    0.04    		 +0.04
    0.06    		 +0.06
    0.08    		 +0.08
    0.10    		 +0.12
    0.12    		 +0.18
    0.18
    Over 2 1/2 in. to 4 in., incl. +0.04
    0.06    		 +0.06
    0.08    		 +0.08
    0.10    		 +0.10
    0.14    		 +0.16
    0.16    		 +0.20
    0.20
    Over 4 in. to 6 in., incl. +0.06
    0.10    		 +0.08
    0.10    		 +0.10
    0.10    		 +0.12
    0.16    		 +0.18
    0.18    		 +0.22
    0.22
    Longer than 6 in. +0.10
    0.18    		 +0.12
    0.18    		 +0.14
    0.18    		 +0.16
    0.20    		 +0.22
    0.22    		 +0.24
    0.24
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