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    2. ASME B18.2.4.1M Metric Hex Nuts (Style 1) Dimensional Data

    ASME B18.2.4.1M Metric Hex Nuts (Style 1) Dimensional Data

    ASME B18.2.4.1M Metric Hex Nut specifications define the essential dimensional data for American National Standard metric hex nuts, Style 1, for coarse thread assemblies.
    The ongoing globalization of manufacturing, aerospace, and supply chain integration has cemented metric fasteners as the unequivocally dominant standard in modern mechanical design.
    To support this paradigm in North America, the ASME B18.2.4.1M specification was developed to address and standardize the dimensional limits for "Style 1" metric hex nuts.
    In the specific terminology of metric fastening, a "Style 1" nut denotes a standard-height geometry, representing the default, mathematically optimized proportion of vertical thickness to nominal thread diameter used in the vast majority of non-specialized engineering applications.
    This is designed in contrast to Style 2 (governed by ASME B18.2.4.2M), which features an intentionally taller profile necessary to withstand the extreme proof loads characteristic of property class 9 and 12 high-strength assemblies.
    The exhaustive ASME B18.2.4.1M standard governs a massive spectrum of nuts, ranging from microminiature M1.6 sizes used in delicate electronics, all the way up to massive M36 heavy-duty variants utilized in earth-moving equipment.
    A highly critical component of this standard is its exact control over the bearing surface dynamics, which ensures that clamping force is translated uniformly into the joined materials.
    The standard specifies that sizes M16 and smaller must be double chamfered to prevent sharp edge interference and eliminate orientation errors during high-speed automated assembly.
    Larger sizes (M20 and above), however, are granted the manufacturer's option to feature either double chamfers or a specific washer-faced bearing surface with a chamfered top.
    The dimensional runout of this bearing face with respect to the thread pitch diameter must remain tightly constrained; excessive runout forces eccentric loading onto the bolt shank, which can induce severe fatigue stresses and lead to premature catastrophic failure over time.
    Engineers referencing this standard must also account for internal thread tolerance classes.
    ASME B18.2.4.1M explicitly specifies metric coarse threads conforming to a 6H tolerance class in accordance with ASME B1.13M.
    Furthermore, the standard recognizes the realities of material science and manufacturing methods: the maximum Width Across Flats (WAF) dimension is allowed to exceed tabulated values to accommodate the standard commercial tolerances of drawn or rolled bar stock material, specifically when milled-from-bar nonferrous materials are utilized.

    ASME B18.2.4.1M Metric Hex Nut Style 1 Dimensions

    ASME B18.2.4.1M Metric Hex Nut Style 1

    Nominal Dia. S E M Dw C Total Runout of Bearing Surface FIM
    Width Across Flats Width Across Corners Thickness Bearing Face Dia Washer Face Thickness
    Max. Min. Max. Min. Max. Min. Min. Max. Min. Max.
    M1.6 3.20 3.02 3.70 3.41 1.30 1.05 2.3 ... ... ...
    M2 4.00 3.82 4.62 4.32 1.60 1.35 3.1 ... ... ...
    M2.5 5.00 4.82 5.77 5.45 2.00 1.75 4.1 ... ... ...
    M3 5.50 5.32 6.35 6.01 2.40 2.15 4.6 ... ... ...
    M3.5 6.00 5.82 6.93 6.58 2.80 2.55 5.1 ... ... ...
    M4 7.00 6.78 8.08 7.66 3.20 2.90 6.0 ... ... ...
    M5 8.00 7.78 9.24 8.79 4.70 4.40 7.0 ... ... 0.30
    M6 10.00 9.78 11.55 11.05 5.20 4.90 8.9 ... ... 0.33
    M8 13.00 12.73 15.01 14.38 6.80 6.44 11.6 ... ... 0.36
    M10 15.00 14.73 17.32 16.64 9.10 8.70 13.6 ... ... 0.39
    M10 16.00 15.73 18.45 17.77 8.40 8.04 14.6 ... ... 0.39
    M12 18.00 17.73 20.78 20.03 10.80 10.37 16.6 ... ... 0.42
    M14 21.00 20.67 24.25 23.35 12.80 12.10 19.4 ... ... 0.45
    M16 24.00 23.67 27.71 26.75 14.80 14.10 22.4 ... ... 0.48
    M20 30.00 29.16 34.64 32.95 18.00 16.90 27.9 0.8 0.4 0.56
    M24 36.00 35.00 41.57 39.55 21.50 20.20 32.5 0.8 0.4 0.64
    M30 46.00 45.00 53.12 50.85 25.60 24.30 42.5 0.8 0.4 0.76
    M36 55.00 53.80 63.51 60.79 31.00 29.40 50.8 0.8 0.4 0.89
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