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.
Dane,
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.
Why do you add two to the radial lines on a bolt for the grade? 3 lines for a grade 5, 6 lines for a grade 8? Why?
@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.
I have a 1/4-28 cap screw with 6 lines with JH in the center what is this telling grade 8 what about the JH
@Larry- JH refers to Jinn-Her, the Chinese manufacturer 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.