• View PDF
    Standard
  • 0091-22-66157017
  • info@torqbolt.com
    • Home
    2. ASME B18.2.3.1M Metric Hex Cap Screws

    ASTM A1082 Metric Hex Cap Screws: ASME B18.2.3.1M Dimensions

    Precision Metric Cap Screws with Controlled Bearing Surface for Global Industrial and Mechanical Bolted Assemblies.

    ASME B18.2.3.1M Metric Hex Cap Screws are metric-series fasteners that establish comprehensive dimensional requirements for hexagonal head cap screws in SI units, covering head height, width across flats, width across corners, washer face, body diameter, thread pitch, thread length, bearing surface runout, and all associated dimensional tolerances, making them the standard reference for metric hex cap screw procurement in North American-designed systems operating under metric engineering standards and global supply chains. These screws differ from metric hex bolts in their closer body diameter tolerances, mandatory washer face bearing surface, and more controlled head dimensions, giving them superior clamping performance in precision mechanical and process equipment applications. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, these metric hex cap screws provide the combination of metric dimensional precision and outstanding corrosion resistance required for pharmaceutical machinery, food processing equipment, marine instrument enclosures, architectural cladding systems, and chemical plant mechanical assemblies. ASTM A1082 stainless steel metric hex cap screws are dimensionally compatible with ISO 4032 and ISO 4033 metric hexagon nuts, enabling fully corrosion-resistant metric bolted assemblies using matched stainless steel fastener components. Full EN 10204 Type 3.1 material test reports are available for all lots to support quality-controlled project procurement and inspection requirements.

    ASME B18.2.3.1m Metric Hex Cap Screws

    ASME B18.2.3.1m Metric Hex Cap Screws Dimensions

    Nominal Dia.,D,and Thread Pitch Body Dia., D s Width Across Flats, S Width Across Corners, E Head Height, K Wrenching Height, K1 1 Washer Face Thick., C Washer Face Dia., DW
    Max Min. Max Min. Max Min. Max Min. Min. Max Min. Min.
    M5 5 4.82 8 7.78 9.24 8.79 3.65 3.35 2.4 0.5 0.2 7
    M6 6 5.82 10 9.78 11.55 11.05 4.15 3.85 2.8 0.5 0.2 8.9
    M8 8 7.78 13 12.73 15.01 14.38 5.5 5.1 3.7 0.6 0.3 11.6
    aM10 10 9.78 15 14.73 17.32 16.64 6.63 6.17 4.5 0.6 0.3 13.6
    M10 10 9.78 16 15.73 18.48 17.77 6.63 6.17 4.5 0.6 0.3 14.6
    M12 12 11.73 18 17.73 20.78 20.03 7.76 7.24 5.2 0.6 0.3 16.6
    M14 14 13.73 21 20.67 24.25 23.35 9.09 8.51 6.2 0.6 0.3 19.6
    M16 16 15.73 24 23.67 27.71 26.75 10.32 9.68 7 0.8 0.4 22.5
    M20 20 19.67 30 29.16 34.64 32.95 12.88 12.12 8.8 0.8 0.4 27.7
    M24 24 23.67 36 35 41.57 39.55 15.44 14.56 10.5 0.8 0.4 33.2
    M30 30 29.67 46 45 53.12 50.85 19.48 17.92 13.1 0.8 0.4 42.7
    M36 36 35.61 55 53.8 63.51 60.79 23.38 21.62 15.8 0.8 0.4 51.1
    M42 42 41.38 65 62.9 75.06 71.71 26.97 25.03 18.2 1 0.5 59.8
    M48 48 47.38 75 72.6 86.6 82.76 31.07 28.93 21 1 0.5 69
    M56 56 55.26 85 82.2 98.15 93.71 36.2 33.8 24.5 1 0.5 78.1
    M64 64 63.26 95 91.8 109.7 104.65 41.32 38.68 28 1 0.5 87.2
    M72 72 71.26 105 101.4 121.24 115.6 46.45 43.55 31.5 1.2 0.6 96.3
    M80 80 79.26 115 111 132.72 126.54 51.58 48.42 35 1.2 0.6 105.4
    M90 90 89.13 130 125.5 150.11 143.07 57.74 54.26 39.2 1.2 0.6 119.2
    M100 100 99.13 145 140 167.43 159.6 63.9 60.1 43.4 1.2 0.6 133
    • (a) This size with width across flats of 15 mm is not an ISO standard. Unless specifically ordered, M10 hex
    • cap screws with 16 mm width across flats will be furnished.
    • All dimensions are in millimeters.
    • Basic thread length, B, is a reference dimension given in the Thread Length table below (Table 7 of the Standard).
    • Transition thread length, X, includes the length of incomplete threads and tolerances on grip gaging
    • length and body length. It is intended for calculation purposes.
    • For additional manufacturing and acceptance specifications, reference should be made to the
    • ASME B18.2.3.1M-1999.
    ASME B18.2.3.1m Metric Hex Cap Screws

    Nominal
    Screw Diameter
    and
    Thread Pitch    		 Fillet Transition Diameter,
    Da    		 Fillet Length, Lf Fillet
    Radius for
    Short and
    Long
    Screws,
    R, Min.    		 Body
    Diameter
    for Short
    Screws,
    Dsi, Min.
    For Short
    Screws,
    Min.    		 For Short
    and Long
    Screws,
    Max.    		 For Long
    Screws,
    Max.    		 For Short
    Screws, Max.
    M5 5.1 5.7 1.2 0.7 0.2 4.36
    M6 6.2 6.8 1.4 0.9 0.25 5.21
    M8 8.3 9.2 2.0 1.1 0.4 7.04
    M10 10.2 11.2 2.0 1.2 0.4 8.86
    M12 12.2 13.7 3.0 1.3 0.6 10.68
    M14 14.1 15.7 3.0 1.4 0.6 12.50
    M16 16.5 17.7 3.0 1.6 0.6 14.50
    M20 20.7 22.4 4.0 2.1 0.8 18.16
    M24 24.5 26.4 4.0 2.3 0.8 21.80
    M30 30.8 33.4 6.0 3.0 1.0 27.46
    M36 36.6 39.4 6.0 3.1 1.0 33.12
    M42 . . . 45.6 8.0 3.4 1.2 38.78
    M48 . . . 52.6 10.0 4.0 1.6 44.43
    M56 . . . 63.0 12.0 4.8 2.0 52.09
    M64 . . . 71.0 13.0 5.0 2.0 59.74
    M72 . . . 79.0 13.0 5.0 2.0 67.74
    M80 . . . 87.0 13.0 5.0 2.0 75.74
    M90 . . . 97.0 13.0 5.0 2.5 85.74
    M100 . . . 107.0 13.0 5.5 2.5 95.72

    ASME B18.2.3.1m Metric Hex Cap Screws Thread Length

    Nominal Screw Diameter and Thread Pitch Thread Length, B, Ref Transition Thread Length, X, Ref Screws Threaded Full Length
    Screw Lengths, L ≤ 125 Screw Lengths, L > 125 & ≤ 200 Screw Lengths, L > 200 Screw Lengths, L, Under Unthreaded Length Under Head, A, Max. [Note (1)] Screw Lengths, L Unthreaded Length Under Head, A,
    Max.
    At Least Under
    M5 16 22 35 4.0 10 1.2 10 25 2.4
    M6 18 24 37 5.0 12 1.5 12 30 3.0
    M8 22 28 41 6.25 16 1.9 16 40 4.0
    M10 26 32 45 7.5 20 2.2 20 45 4.5
    M12 30 36 49 8.75 24 2.6 24 50 5.3
    M14 34 40 53 10.0 28 3.0 28 60 6.0
    M16 38 44 57 10.0 32 3.0 32 65 6.0
    M20 46 52 65 12.5 40 3.8 40 80 7.5
    M24 54 60 73 15.0 ... ... ... 90 9.0
    M30 66 72 85 17.5 ... ... ... 110 10.5
    M36 ... 84 97 20.0 ... ... ... 140 12.0
    M42 ... 96 109 22.5 ... ... ... 160 13.5
    M48 ... 108 121 25.0 ... ... ... 180 15.0
    M56 ... ... 137 27.5 ... ... ... 220 16.5
    M64 ... ... 153 30.0 ... ... ... 260 18.0
    M72 ... ... 169 30.0 ... ... ... 280 18.0
    M80 ... ... 185 30.0 ... ... ... 300 18.0
    M90 ... ... 205 30.0 ... ... ... 340 18.0
    M100 ... ... 225 30.0 ... ... ... 360 18.0

    ASME B18.2.3.1m Metric Hex Cap Screws Length Tolerance

    Nominal Length Nominal Screw Diameter
    Over Thru M5 M6 M8 M10 M12 M14 M16-M24 >M24
    6 10 ±0.29 ±0.29 ±0.29 ±0.29 ... ... ... ...
    10 18 ±0.35 ±0.35 ±0.35 ±0.35 ±0.35 ±0.35 ±0.35 ...
    18 30 ±0.42 ±0.42 ±0.42 ±0.42 ±0.42 ±0.42 ±0.42 ±1.05
    30 50 ±0.50 ±0.50 ±0.50 ±0.50 ±0.50 ±0.50 ±0.50 ±1.25
    50 60 ±1.50 ±0.60 ±0.60 ±0.60 ±0.60 ±0.60 ±0.60 ±1.50
    60 80 ±1.50 ±1.50 ±0.60 ±0.60 ±0.60 ±0.60 ±0.60 ±1.50
    80 100 ±1.75 ±1.75 ±1.75 ±0.70 ±0.70 ±0.70 ±0.70 ±1.75
    100 120 ±1.75 ±1.75 ±1.75 ±1.75 ±0.70 ±0.70 ±0.70 ±1.75
    120 140 ±2.00 ±2.00 ±2.00 ±2.00 ±2.00 ±0.80 ±0.80 ±2.00
    140 150 ±2.00 ±2.00 ±2.00 ±2.00 ±2.00 ±2.00 ±0.80 ±2.00
    150 180 ±2.00 ±2.00 ±2.00 ±2.00 ±2.00 ±2.00 ±2.00 ±2.00
    180 250 ±2.30 ±2.30 ±2.30 ±2.30 ±2.30 ±2.30 ±2.30 ±2.30
    250 315 ±2.60 ±2.60 ±2.60 ±2.60 ±2.60 ±2.60 ±2.60 ±2.60
    315 400 ±2.85 ±2.85 ±2.85 ±2.85 ±2.85 ±2.85 ±2.85 ±2.85
    400 500 ±3.15 ±3.15 ±3.15 ±3.15 ±3.15 ±3.15 ±3.15 ±3.15

    Frequently Asked Questions

    Which stainless steel grades does ASTM A1082 cover for metric hex cap screws?

    ASTM A1082/A1082M (2016) Table 1 lists 14 duplex (ferritic-austenitic) grades, S31100, S31260, S31803, S32101, S32202, S32205 (2205), S32304 (2304), S32506, S32550 (255), S32750 (2507), S32760, S32906, S32950 and S39277, and 5 precipitation-hardening grades, S15700 (Type 632), S17400 (Type 630), S17600 (Type 635), S17700 (Type 631) and S35500 (Type 634). Grade selection depends on design, service conditions and the mechanical properties required.

    Which standard sets the dimensions of these metric hex cap screws?

    Dimensions follow ASME B18.2.3.1M, tabulated on this page. ASTM A1082/A1082M sets chemistry (Table 1), heat treatment and mechanical properties (Tables 2 to 4) and marking (Table 5). ASTM A962/A962M general requirements also apply, and A1082 prevails where the two conflict (clause 4.1). Inch-pound units apply unless the order specifies A1082M (clause 1.4).

    Can ASTM A1082 metric hex cap screws be used in sour service (NACE MR0175 / ISO 15156)?

    ISO 15156-3 Table A.24 accepts wrought duplex stainless steel for any equipment when it is solution-annealed and liquid-quenched or rapidly cooled, has 35 % to 65 % ferrite and has had no ageing heat treatment. With 30 ≤ PREN ≤ 40 and Mo ≥ 1.5 % the limit is 232 °C (450 °F) and 10 kPa (1.5 psi) H2S partial pressure; with 40 < PREN ≤ 45 it is 232 °C (450 °F) and 20 kPa (3 psi). Table A.27 accepts wrought 17-4 PH (S17400) at 33 HRC max after a double age at 620 °C (1150 °F) or a modified double age, for named wellhead, valve and subsurface components, up to 3.4 kPa (0.5 psi) H2S and pH 4.5 or above.

    How are ASTM A1082 metric hex cap screws marked?

    The grade symbol comes from Table 5 (clause 11.1), for example 32205 for S32205 or 174G for S17400 in H1150. With Supplementary Requirement S2 the marking goes on the heads of bolts of all sizes; if the area is too small, the grade symbol may go on one end and the manufacturer's identification on the other. Bolts under 1/4 in. [6 mm] are marked by agreement between purchaser and manufacturer.

    What are the ASTM A1082 requirements for super duplex 2507 (S32750) metric hex cap screws?

    Table 4: solution annealed at 1880 to 2060 °F [1025 to 1125 °C], water quenched. Up to and including 2 in.: tensile 116 ksi [800 MPa] and yield 80 ksi [550 MPa] min. Over 2 in.: 110 ksi [760 MPa] and 75 ksi [515 MPa] min. Elongation 15 % min and hardness 33 HRC or 310 HB max for both. The marking grade symbol is 32750 (Table 5).

    References & Standards

    • ASTM A1082/A1082M: Standard Specification for High Strength Precipitation Hardening and Duplex Stainless Steel Bolting for Special Purpose Applications (2016 edition)
    • ASTM A962/A962M: Specification for Common Requirements for Bolting Intended for Use at Any Temperature from Cryogenic to the Creep Range
    • ASTM A370: Test Methods and Definitions for Mechanical Testing of Steel Products
    • ISO 15156-3 (NACE MR0175/ISO 15156): Cracking-resistant CRAs (corrosion-resistant alloys) and other alloys for H2S-containing environments in oil and gas production
    • ASME B18.2.3.1M: dimensional standard for the metric hex cap screws tabulated on this page
    Related Specifications
    Surface Treatments
    Certifications
    About Us
    Questions? Contact us.
    Showcase of our Microsites.
    Satisfaction Survey

    survey

    TUVRheinland CERTIFIED

    © TorqBolt P(Ltd) · Built with in INDIA.