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.

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    MNP is Michigan Nut Products Corp of Utica, MI
    CP is Chandler Products of USA
    I have a question, who uses the atomic head stamp of three oval circles on top of each other 120 degrees apart?

    @Herb- Sorry, but we looked through our head marking information and did not immediately find the head mark you describe.

    I’ve looked through the patent office registered manufacture head insignia however I cannot locate E
    I’m restoring an antique oak dining table and there are 4 bolts with the letter E
    Any idea or point in the right direction would be appreciated!

    @Karen- I looked through an old head marking catalog and found several manufacturers who all use ‘E’. I am not terribly familiar with any of these companies and so do not know if any are still in business. E&E Fastener in Michigan. Eagan Machine in Connecticut. Ellis Precision in Texas. Engineering Materials Co in California. Erico Fastening in New Jersey. Erie Bolt in Pennsylvania. Erie Manufacturing in Texas. ESMET in Ohio. Euclid Industries in Ohio. Good luck.

    I have a bolt taken from my triumph bonnivale it has nf stamped on it. I need a replacement but slightly longer. I have tried all suppliers christchurch Dorset area. Nobody can help me with this

    @Phil- Apologies, but we do not handle any automotive fasteners. Perhaps a local machine shop can help with this special.

    Check out the Brittish Standard specifications for National Fine threads. They are often close to metric so don’t get them mixed up.

    I have a large eye bolt with a 1-1/2 NC thread pitch, no shoulder. There is a “B” in a diamond shape on the top and on the bottom of the eye it says “H3175”. Can you supply me with the manufacturer?

    @Teri- We are familiar with a eye bolt manufacturer that uses a diamond and a ‘D’-that is Edward W Daniel, but we do not know who uses the same design with a ‘B’.

    I was wandering if anyone knows why /or has also found a bolt with a swastika on it ….I found a couple at work and thought it a little more than odd???

    Is there a way to determine a bolts material from looking at it? For example, we generally need hardware that is both corrosion resistant and non-magnetic. (Any 300 series stainless would be sufficient. )

    @Dave- Many fastener grades require head markings that will also indicate the chemistry. Examples of head markings for 300 series stainless are ASTM A193/A320 B8 (304) or B8M (316) which are marked B8/B8M respectively. There is also ASTM F593 which has many several head markings that all indicate 300 series stainless. Details can be found on our F593 page In addition to these ASTM grades, bolts that are not made to a bolt specification are sometimes marked with the steel they are made from. For example we have seen bolts marked 30400 or 31600 to indicate they they are made from 304 or 316 stainless steel. If the bolt is not marked with any of the above, then you would need to have a chemical analysis performed to see what steel was used.

    we are looking at an older tower with square head galv bolts, no head markings.
    Would you use grade 2.
    Karl Tashjian

    @Karl- With no markings, I’d assume it was made to grade 2 or some low carbon, ungraded equivalent. You should be safe moving forward with grade 2.

    To Rebecca, who asked a question on August 10, 2017 at 5:00 pm. I’m sorry this response is over a year late, but I’ve only just found your (hitherto unanswered) question. You were looking for information about a bolt which has its head marked SB R. The “SB” refers to an Indian manufacturer specialising in imperial fasteners sizes – specifically BSF thread sizes (British Standard Fine).

    The “R” on your bolt head relates to a tensile strength code system used specifically for BSF fasteners. “R” tells us that the tensile strength of your fastener is the approximate equivalent of a “grade F” or “grade 5” fastener. In other words, if your bolt was not a BSF fastener, then its head would be stamped in accordance with the grade F (or grade 5) coding system – which would be three lines radiating from the centre of the bolt head at 120 degree intervals.

    Rather late for the OP, but I hope this might help somebody!



    @Ken- We assume that it was done for simplicity, but those markings were decided upon decades ago and we are not sure why the members of the committee decided as they did.

    Greetings. I have on old brush hog maybe from the 1950’s. It has a bolt functioning as a shear bolt. The bolt is 1/2″ diameter, and it has a diamond design in the center of the head. I think I can discern a 2 offset form the diamond to the lower left. I am hoping for confirmation that this particular bolt is a grade 2 and appropriate to function as a shear bolt. I am considering replacing it with a shear bolt bought at Tractor Supply to be safe.

    @Charles- The marking requirement for SAE grade 2 bolts is nothing, no mark. If your bolt has a ‘2’ on it, that could mean a lot of things, as there are many bolts that are manufactured with special marks per customer request. Grade 2 is the lowest grade commonly available, so what you have is likely not weaker than grade 2. However, if you are unsure, replacing it with a known grade may be worth the peace of mind.

    Is this thread still open? I disassembling an old bench vise to restore it we came across a square head bolt marked with a swastika inside a triangle over the letters KI. The other screws and bolts in the vise are unmarked, as is the outside. Any idea who made it and what (if anything) the markings mean?

    @Chris- Sorry, we don’t have any idea as to the manufacturer. The swastika would of course make us think they were made in Germany in the 30’s or 40’s, but beyond that we do not know.

    I have a portable generator that has bolts contaning 6 lines at the top and the numbers 8.2 in the center. Are these considered high strength fasteners and are they suspect/counterfeit cuz there are no mfg head markings?

    @Rich – The six radial lines mean than the bolts are either SAE J429 grade 8 or grade 8.2 depending on the configuration of the lines. Normally the 8.2 is not added, but in this case it appears to be so I would have to assume that 8.2 is the grade. As for the counterfeit question, anything is possible, but it is more likely that the generator manufacturer had bolts made that did not have the manufacturer’s ID. We manufacture private label bolts with custom (or no) head markings.

    Hello, I have a hex bolt with the markings SB on one end of the bolt head and then R on the opposite end of the bolt head. I’m trying to find the manufacturer or a location to buy more but the local hardware stores I’ve visited say the bolt is not US or metric standard. Would you happen to know what those letters represent? Thank you.

    I broke one of the bolts attaching my caliper bracket to the wheel assembly on my car. Because brakes are perhaps the most critical application in the car, I am very eager to replace it with a bolt of the correct strength grade. I am very familiar with standards in the industrial setting, but this particular bolt is perplexing me. The head is slightly recessed in the center (concave), featuring an almost centered 6 above a single dot, or perhaps a 9 beneath a single dot. I would normally buy an OEM replacement, but unfortunately it seems they are not offered by the dealer even, and I have had no luck with auto parts shops. Any insight you can provide is most welcome!

    @Kevin- Our only guess is that it might be a grade 9, which is used in many OEM and automotive applications. We do not sell such items, but most auto parts stores would likely have them.

    A very heavy duty, large industrial bolt fell out of nowhere and landed on the roof of my car while driving down the interstate. It caused damage and pierced into the interior of my car so I had to get a whole new roof installed. It has an “LE” on the head. Do you know what this type of bolt is used for or where it came from? Thank you!

    @Carol- We are sorry to hear about your accident. “LE” bolts are manufactured by Lake Erie Products. They make many grades and types of bolts, so it is hard to determine what type that is without more information and/or a photo.

    I have a question for a bolt expert, we have a bolt here that is a 1/2″x7″ galvanized square headed bolt with a T stamped in the head, we are wondering who the manufacturer may be

    Thanks, Doug

    @Doug- We found several different manufacturers whose head mark was a ‘T’. We wouldn’t be able to narrow it down any more without a photo. If you’d like, you can email one to and we’d be happy to look at it.

    @Chris – Apologies, but we looked through our list of head marks, but were unable to locate OF.

    Does anyone know what manufacturer head marking is 3 dots in a triangle shape. I have an indented hex head flange screw with 10.9 stamped in the middle and 3 dots around it in a triangle shape. One at the top and two at the bottom. Any help would be appreciated. Thanks!

    @Ali- We looked through our list of manufacturing identifications and were unable to find the markings you describe.

    The local Tractor Supply sells a 1/2″x3″ hex head bolt (19mm) that has HFG stamped in the center and an unusual stamp below it, more like a symbol than letter. No radial lines. Is this a grade 2 bolt? Store employees do not seem to know.

    @Stuart- Our guess is that your bolt is an SAE grade 2 bolt. Most other SAE and ASTM grades require grade marking, so in the absence of that, grade 2 seems like the most likely grade. As for the HFS and symbol, that is more than likely the manufacturer’s stamp. I’d assume the symbol is part of that.

    If it is a bolt from tractor supply bulk bins they are a grade 2 if the bolt has a gold color that is the grade 8

    @Chase- Yes, grade 8 bolts are usually yellow zinc plated, but that in itself is not an indicator of grade, since you could yellow zinc plate any grade. The head markings will indicate the grade, the plating is purely aesthetic.

    I have a bolt, with 3 grade 5 hash marks around the outside, and a triangle that swirls into the center. What kind of bolt is this?

    @Mike- The three hash marks indicate grade 5, the triangle with a swirl is the manufacturer’s stamp for Bowman Distribution. They are a distributor that has private label bolts made with their head mark.

    I have a bolt with HCZ and 3 hash marks with a line through them below that? is this a grade 5 or standard ya think?

    @John- Yes, the three radial lines indicate that the bolt is SAE grade 5. The HCZ would be the manufacturer’s identification.

    @Dale- 8.8 is a common grade of metric fastener that is similar in strength to an SAE grade 5 or ASTM A449 bolt.

    On a CSA explosion proof box do grade 5 NDF bolts meet electrical standard or are they always required to be grade 8 for 1/2″ and below.


    I came across some square head lag bolts where the only marking is a U on the head. They are also a golden yellowish material.. Any ideas on what I have.

    @Brad- I would assume that the U is a manufacturer’s marking. Lag bolts are not typically graded, so since there are no grade marks non your bolt I would have to say it is just low carbon, mild steel.

    @AJ- We are not sure why the writers of the SAE J429 standard decided to require the number of lines that they did. The standard was written decades ago.

    Since no marks (zero marks) indicates a grade 2 fastener, just 2 to the number of marks on a bolt head to arrive at the grade of the bolt.

    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?

    @Craig- BT is likely the manufacturer’s ID mark, but I am unfamiliar with who that might be.

    @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?


    @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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