>When somebody refers to a Schedule 8 bolt, what are they referring to
This is an SAE (Society of Automotive Engineers) grading system for bolts.
There is a grade 1 or 2 that has no marks on the head, grade 5 which has 3
equally spaced marks, and grade 8 which has 6 equally spaced marks. There
are some other SAE grades such as 3 marks all in the upper semi-circle, 5
marks equally spaced, 7 marks in one semi-circle, etc. There is also an
ASTM (American Society for Testing and Materials) bolt grading system which
has various combinations of marks and numbers. Of interest is that the SAE
and the ASTM systems overlap and both use the same head markings for bolts
of the 5 and 8 grade, although ASTM calls them A449 and A354BD, they are
still marked with 3 or 6 marks. Basically a grade 5 fastener is made from
medium carbon steel that has been heat treated to Rc30 and grade 8's are
made from alloy steel which is heat treated to Rc36, meaning that both can
be drilled, cut, milled ,etc with conventional HSS cutting tools. The proof
strength for a grade 5 is typically 85kpsi and for a grade 8 it is 120kpsi.
Proof strength is a safer number to use rather than tensile strength or
yield strength as the latter two are determined at or near the point of
failure. Just for the heck of it, a metric grade 8.8 is in the same
strength range as a grade 5 and a metric 10.9 is in the same range as a grade 8.
After all that, did I answer the question?
je
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