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.
Why did SAE make 3 lines mean grade 5 and 6 lines mean grade 8.
Why not 5 lines = grade 5 and 8 lines = Grade 8?
@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.
@Rebecca- Apologies, but we are unsure of who that manufacturers’ mark is. You might look through the US Trademark and Patent office website – they have a list of registered head markings. https://www.uspto.gov/sites/default/files/trademarks/law/fastener/FQA_Registry.pdf