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    2. ASME B18.2.1 Heavy Hex Bolts

    ASME B18.2.1 Heavy Hex Bolts Dimensions

    Wide-Head Inch-Series Bolts for High-Load Structural, Flange, and Pipeline Bolted Connections.

    ASME B18.2.1 Heavy Hex Bolts are inch-series fasteners featuring a wider and taller hexagonal head than standard hex bolts, providing an increased bearing surface that distributes clamping load more effectively across the joint and reduces the risk of surface embedment under high preload — making them the preferred choice for heavy structural steel connections, pressure vessel flange bolting, and pipeline assembly joints. The ASME B18.2.1 standard governs all critical dimensional parameters for heavy hex bolts including head height, width across flats, width across corners, body diameter, thread length, fillet radius, and all associated manufacturing tolerances for sizes ranging from 1/4 inch through 4 inches in diameter. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, these bolts deliver excellent tensile strength combined with superior corrosion resistance, making them ideal for coastal structures, chemical processing plants, offshore platforms, and environments where carbon steel bolting would degrade rapidly. The larger head footprint also provides better wrench engagement and torque resistance compared to standard hex bolts, reducing the risk of bolt rotation during installation in high-preload structural bolting applications. Specifying both ASME B18.2.1 for dimensional compliance and ASTM A1082 for material properties ensures a fully defined heavy hex bolt procurement that meets both dimensional and performance requirements.

    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

    Frequently Asked Questions

    What stainless steel grades does ASTM A1082 cover for heavy hex bolts?

    ASTM A1082 covers duplex grades (S31803/2205, S32205/2205, S32750/2507, S32760/Zeron 100, S39277/AL-6XN) and precipitation-hardening grades (S17400/17-4 PH, S17700/17-7 PH, S15700/15-7 PH, S35500/AM-355) - all available for this product family at TorqBolt.

    What is the standard dimensional reference for these heavy hex bolts?

    This product follows ASME B18.2 1, the dimensional standard for heavy hex bolts in stainless steel. Material chemistry, mechanical properties and heat treatment follow ASTM A1082/A1082M. TorqBolt supplies both inch-series and metric sizes per the applicable ASME or ISO drawing.

    Are A1082 heavy hex bolts suitable for sour service (NACE MR0175)?

    Yes, with hardness control. NACE MR0175 / ISO 15156 permits duplex grades S31803, S32205, S32750, S32760 at 28 HRC max for sour service. 17-4 PH (S17400) at H1150 condition (28 HRC) is the most common PH grade qualified for sour service. TorqBolt provides NACE-MR0175 compliant heat-treat reports.

    What is the typical strength of A1082 super-duplex 2507 (S32750) heavy hex bolts?

    Super-duplex 2507 (S32750) per A1082: tensile 116 ksi (800 MPa) min, yield 80 ksi (550 MPa) min, elongation 15% min, 32 HRC max. PREN ≈ 42 - suitable for seawater, brine and chloride-rich pressure-vessel service. Higher strength than austenitic A193 B8M while offering pitting resistance well above 304/316.

    References & Standards

    • ASTM A1082 / A1082M - Standard Specification for High-Strength Precipitation-Hardening and Duplex Stainless Steel Bolting for Special-Purpose Applications (current edition 2016, active)
    • ASTM A962 / A962M - General Requirements for Special-Purpose Bolting Materials
    • ASTM A370 - Mechanical Testing of Steel Products
    • NACE MR0175 / ISO 15156 - Sour-service hardness limits for petroleum & natural gas industries
    • ASME B18 series - Dimensional standards for bolts, screws, nuts, studs
    • ISO 4032 / 4033 / 4035 - Metric hexagon nut dimensional standards
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