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Fastener Head Markings Decoded

Question: Sometimes there are lines on the bolt head. What do they mean?

Grade 5 Head Marking ExampleAnswer: The lines on the head of a bolt indicate its grade. SAE J429 (Society of Automotive Engineers) bolts have radial lines, whereas ASTM (American Society for Testing and Materials) uses a combination of letters and numbers to indicate the grade. Three radial lines will indicate an SAE grade 5 fastener, while six radial lines will indicate an SAE grade 8 fastener. These are the most common grades, but there are others. Our Fastener Identification Markings Chart has a complete list of bolt grades with accompanying head markings.

Posted by Dane McKinnon

Phone: (503) 219-6991 Email: danem@portlandbolt.com
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11 Responses to “Fastener Head Markings Decoded”

  1. Dane McKinnon says:

    @Luke – It is most likely Gaffney Bolt in Illinois, but there are also a few international manufacturers that use a ‘G’, so it hard to say for certain. We’d be happy to look at a photo if you wanted to send one in.

  2. Luke Cowart says:

    Hello, I’ve got a screw with a “G” stamped in the head. Do you know which manufacturer that is?

  3. Dane McKinnon says:

    @Rick – Sorry, I looked through my headmarking information(available from the US Patent and Trademark Office) and was not able to find any reference to EMM. Apologies.

  4. Rick Corcoran says:

    Anyone know the manufacturer with the marking EMM?
    Thank you.

  5. Dane McKinnon says:

    @Paul – I am not sure who’s marking that is, but you may be able to find it listed on the US Patent Office Fastener Insignia Register here http://www.uspto.gov/trademarks/law/FQA_Registry.pdf

  6. Paul Browning says:

    I have some screws with a “Star of David” mark on the top of the head, (2 equilateral triangles superimposed). Which company makes those?

  7. Dane McKinnon says:

    @Michael – That doesn’t ring an immediate bell, but if you want to email in a photo, I’d be happy to see if I can find it. dane@portlandbolt.com

  8. michael says:

    I have a 3/8 nc bolt wilt the marking that looks like a H beam with the letters B and S on each side of it.Can any one ID it.
    Thanks Mike

  9. david krauter says:

    It is the first time I heard about these matters. I am not really keen on these head markings. But I am glad to have known about them.

  10. Jonathan Waltner says:

    @Jess Elliott – That sounds like a manufacturer’s head stamp. For example, our grade 5 bolts look like the image above.

    The US Patent and Trademark Office has a long list of registered manufacturer head insignia. You might take a look at it and see if any of them match the markings on your bolt.

  11. Jess Elliott says:

    We recently received HHCS with “SJ” in addition to the normal three, grade 5 hash marks.

    What does the “SJ” mean? Is it manufacturer or a foreign source material standard?

    Regards,
    Jess

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