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.
I have a bolt with a circle with a capital M or W marked in the circle do you no what brand that would be
@CJ- Apologies, but that head marking is not one that is familiar to us.
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. )
Thanks!!!
@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 https://www.portlandbolt.com/technical/specifications/astm-f593/. 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.
the triangle marking is made by infasco
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!
Regards,
Chris