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bolt markings


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got given some bolts for a job last night

they had three radial marks on them which i believe stands for "Medium Carbon Steel, Quenched and Tempered" they are stamped 7 on the bolt head I can't find any info on that number

anyone know of a website that explains the number figures

many thanks

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got given some bolts for a job last night

they had three radial marks on them which i believe stands for "Medium Carbon Steel, Quenched and Tempered" they are stamped 7 on the bolt head I can't find any info on that number

anyone know of a website that explains the number figures

many thanks

Three radial marks are used to indicate high tensile on UNF bolts at least. Not sure what 7 means, imperial bolts usually have a letter.

Do a Google on "bolt markings" you should find something.

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Three radial marks are used to designate SAE grade 5 (approx equiv to ISO class 8.8). But 7 does not fit with this!

Japanese (JIS standards) mark the centre of bolt heads with a prominent number. With these 7 is commonly used and I have also seen 4, 9 and higher numbers used. An educated guess is that the number is similar to the ISO class (ie 7 may be just below class 8.8 and 9 between classes 8.8 and 10.9).

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As stated above, the three radial markes at 12, 4 & 8 o'clock mean grade 8.8.

The number seven is odd - is it cast on the bolt or stamped on as an afterthought?

For what it's worth, I'd swap them for some from a known source. In your business you don't want to get it wrong! :o

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