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

SAE J429 Grade 5The 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.

Written December 4, 2007 by
Dane McKinnonDane McKinnon

Phone: 503.219.6991
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33 comments

    Hi I have a bolt with 6 dashes on it which I’m assuming is grade 8 and RC stamped on the head also do you know the manufacturer??

    @Brad- RC is the manufacturer’s stamp for Ningbo RuiChang Metal Products in Ningbo, China. And yes, six radial dashes is SAE J429 grade 8.

    Trying to find out what the letters BT on the head of a coach bolt (6mm diameter and approx 70mm length) might be. Any ideas?

    @John- I am sorry, but that does not immediately ring a bell. If you’d like to send in a photo, perhaps we can decode it for you.

    I have a bolt top of head says -FNL
    Center of head Has 9 dashes in the center
    Bottom of the Bolt says G9

    Wondering about the grade of this bolt

    @Jason- FNL is likely the bolt manufacturer, Fastenal. The G9 and nine dashes signify grade 9, which is a high strength grade slightly stronger than SAE grade 8. Grade 9 is a grade that was created to be a high strength alternative to SAE grade 8, but is not covered specifically by SAE J429 nor any other standards organization.

    I have a very old A286 fastener spec that refers to marking codes such as H19 and H28 on the head. We don’t know what that means. Anybody?

    have 1969 vet bolts holding rear spring have a w8 or wb on head corvette supplier sells grade 5 bolt as replacement are these strong enough

    @Paul – I am not familiar with a ‘W8’ or ‘WB’ marking on the head of a bolt, so I am not certain what grade they might be. Sorry we cannot help.

    Rivets removed and replaced with bolts at floorbeam connections on a truss bridge. All bolts and nuts are square….most have no designation, though some have a G in the center and other have an S off center.
    Any idea of strengths?

    @Sammy- Most off the shelf square bolts and nuts are just made from low carbon steel, similar to A307A/grade 2. If they were made to be high strength I would assume that they would have a grade marking of some sort, but the markings you describe do not sound like grade markings. I would assume that G and S are manufacturer’s markings, although they do not sound familiar to me.

    Trying to ID bolt head marking, which I think could be Monel K 500. Hex bolt mark is >.K.
    the dots are on the center line not at foot as shown in this comment.
    Thanks Baz

    @Barry Tyrrell- Apologies, but that mark does not ring a bell with us. Unless the bolt was made to an ASTM, ISO, or SAE standard, I don’t think there is a standard head mark to indicate Monel K 500. Sorry that we cannot help.

    i have a bolt with with A325 stamped on the top and NDF on bottom. Assume the A325 is ASTM a325 spec and NDF is manufacturer. Do you know what NDF stands for? What is the equivalent SAE grade for ASTM A325?

    @Daryl- I am sorry, but I looked thru my list of manufacturing marks, and I do not see NDF anywhere. As for an A325 equivalent, the closest would be SAE J429 grade 5, but I wouldn’t substitute without an engineering approval as they are some key differences.

    @Adeniyi- I am sorry, I do not know. Normally there is both a grade mark, and manufacturer’s ID mark. I am not aware of any grade that matches up with your mark, and I am not familiar with any manufacturer that uses that mark. Apologies.

    @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.

    @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.

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

    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

    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.

    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

    @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.

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