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.
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.
What grade is a bolt coming out of China with a head stamp of 8.8?
@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.
@Dan- We are sorry, but we don’t have familiarity with electrical standards.