What is the difference between ASTM A320 Grade L7 and A320 Grade L7M?

ASTM A320 possesses several fastener grades manufactured from either alloy or stainless steel and are intended for cold temperature applications. Both Grade L7 and L7M are manufactured from a quenched and tempered alloy steel. While the chemical requirements for both Grades L7 and L7M are identical, there are several differences that separate the two grades.

Grade Yield, ksi, min Tensile, ksi, min Tempering temp, F, min Hardness, max
L7 105 125 1100 321 HB/35 HRC
L7M 80 100 1150 235 HB/99 HRB

Grade L7 bolts are significantly higher in strength than Grade L7m bolts.  Additionally, it is important to note that a requirement unique to L7M fasteners is that every part needs to undergo a hardness test. The compatible nut for an L7M bolt, ASTM A194 Grade 7M, also requires hardness test of each part. Machining the Grade 7M nuts after heat treating is prohibited.

A320 Grade L7 fasteners require a permanent marking of “L7” on bolt heads and one end of rods, while Grade L7M fasteners are marked “L7M”. Compatible nuts for both grades that have been impact tested are marked with the letter “L”.

If you have any additional questions or need a quote, please contact our team and we will be more than happy to assist you.

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    @Greg- Yes, A193 B7 is typically specified for high temperatures and A320 L7 is typically for low temperatures.

    @Ardian- If you can let us know the quantity, sizes, finish and need date for your L7 bolts, we are happy to get you a quote.

    Approved Isometric Drawing stud bolt SA-302 Gr L7 but installed SA-302 Gr L7N. Which stud bolts is higher grade, SA-302 Gr L7 or SA-302 Gr L7N?

    @Zaid- SA320 (SA302 is not a fastener standard) includes a grade L7 and and L7M, those differences are outlined in this FAQ. There is not a grade L7N within the A320 standard.

    Nuts supplied as per ASTM A194 Gr.2H with Bolting material SA-320 Gr.L7 required marking with additional letter “L” if impact tested.

    @Faiz- The ‘L’ marking for charpy tested A194 nuts applies only to grades 7 and 7M nuts, not to grade 2H.

    Good morning , hope you can help me out in a jam. I am looking for:
    2pcs of L7M 1”-8 threaded studs 10” in length
    Thank You

    @Tushar- Yes, the A320 standard requires that A194 nuts used with A320 bolts shall be charpy impact tested.

    @Apurva- We are able to supply L7 or L7M, but it is not possible to dual certify those grades as they do not have the same requirements.

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