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    2. Grade 8M Nuts

    ASTM A194 Grade 8M Heavy Hex Nuts — UNS S31600

    Marine-grade stainless steel heavy hex nuts with superior corrosion resistance.

    ASTM A194/A194M Grade 8M Nuts are molybdenum-bearing stainless steel fasteners designed for superior resistance against chlorides, chemicals, and seawater exposure. These heavy hex nuts are ideal for offshore, marine, desalination, and pharmaceutical applications. Grade 8M nuts are commonly matched with ASTM A193/A193M stainless steel stud bolts for highly corrosive service conditions. ASTM A320/A320M low-temperature bolting systems, ASTM A563M structural standards, and ASTM F2437/F2437M fastening applications are also frequently associated with these nuts.

    ASTM A194/A194M Gr 8M Chemical Requirements

    Grade Description
    and
    UNS Designation    		 C Mn P SE Si Cr Ni Mo
    ASTM A194/A194M Grade 8M (316) S31600 0.08 2.00 0.045 0.030 1.00 16.0-18.0 10.0-14.0 2.00-3.00
    • (A) Total aluminum, soluble and insoluble.
    • (B) Maximum, unless minimum or range is indicated.
    • (C) Where ellipses (...) appear in this table there is no requirement.

    ASTM A194/A194M Gr 8M Hardness Requirements

    Grade and Type Completed Nuts
    Brinell Hardness Rockwell Hardness
    C Scale B Scale
    ASTM A194/A194M Grade 8M 126 to 300 32 max 60 min

    ASTM A194/A194M Gr 8M Proof Load Requirements (Inch Series)

    Nominal Size, in. Threads per Inch Stress Area in. 2 Proof Load, lbf A
    Grade 8M
    Heavy HexH HexI
    1/4 20 0.0316 2 540 2 380
    5/16 18 0.0524 4 190 3 930
    3/8 16 0.0774 6 200 5 810
    7/16 14 0.1063 8 500 7 970
    1/2 13 0.1419 11 350 10 640
    9/16 12 0.182 14 560 13 650
    5/8 11 0.226 18 080 16 950
    3/4 10 0.334 26 720 25 050
    7/8 9 0.462 36 960 34 650
    1 8 0.606 48 480 45 450
    11/8 8 0.790 63 200 59 250
    11/4 8 1.000 80 000 75 000
    13/8 8 1.233 98 640 92 450
    11/2 8 1.492 119 360 111 900
    • (A) See limit for proof load test in 8.2.2.1. The proof load for jam nuts shall be 46 % of the tabulated load.
    • (B) Based on proof stress of 130 000 psi.
    • (C) Based on proof stress of 120 000 psi.
    • (D) Based on proof stress of 150 000 psi.
    • (E) Based on proof stress of 135 000 psi.
    • (F) Based on proof stress of 175 000 psi.
    • (G) Based on proof stress of 150 000 psi.
    • (H) Based on proof stress of 80 000 psi.
    • (I) Based on proof stress of 75 000 psi.

    ASTM A194/A194M Gr 8M Proof Load Requirements (Metric Series)

    Nominal Size, mm Threads Pitch Stress Area mm 2 Proof Load, kNA
    Grade 8M
    Heavy HexH HexI
    M6 1.0 20.1 11.1 10.4
    M8 1.25 36.6 20.1 18.8
    M10 1.50 58.0 31.9 29.9
    M12 1.75 84.3 46.4 43.4
    M14 2.0 115.0 63.3 59.2
    M16 2.0 157.0 86.4 80.9
    M20 2.5 245.0 134.8 126.2
    M22 2.5 303.0 166.7 156.0
    M24 3.0 353.0 194.2 181.8
    M27 3.0 459.0 252.5 236.4
    M30 3.5 561.0 308.6 288.9
    M36 4.0 817.0 449.4 420.8
    • (A) See limit for proof load test in 8.2.2.1. The proof load for jam nuts shall be 46 % of the tabulated load.
    • (B) Based on proof stress of 895 MPa.
    • (C) Based on proof stress of 825 MPa.
    • (D) Based on proof stress of 1035 MPa.
    • (E) Based on proof stress of 930 MPa.
    • (F) Based on proof stress of 1205 MPa.
    • (G) Based on proof stress of 1035 MPa.
    • (H) Based on proof stress of 550 MPa.
    • (I) Based on proof stress of 515 MPa.

    Related Grades & References

    Grade 8M is solution-treated Type 316 molybdenum-bearing stainless (UNS S31600), offering superior chloride-pitting resistance over Grade 8 (304), preferred for marine, brine, and acidic chloride service paired with A193 B8M studs. Class 1A finished-condition variant: Grade 8MA. For 304-equivalent corrosion resistance at lower cost, use Grade 8. Low-carbon 316LN nitrogen-strengthened: Grade 8MLN. For nitrogen-strengthened 316N: Grade 8MN. Super-austenitic 254 SMO: Grade 8MLCUN. Dimensions: ASME B18.2.2. Reference: ASTM A194 PDF · A194 hub.

    International Equivalents

    StandardRegionNotes
    ASTM F593 Group 2USA316 stainless fastener (general)
    ASTM A194-8MAUSAClass 1A finished condition variant
    BS EN 10088-3 1.4401EUAustenitic 316 stainless
    DIN X5CrNiMo17-12-2GermanyMaterial number 1.4401 (316)
    ISO 3506-2 A4-70ISOClass A4 Mo-bearing stainless nut
    JIS SUS316JapanType 316 molybdenum-bearing austenitic
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