In a message dated 9/24/2001 9:33:59 AM Eastern Daylight Time, Ajhsys@aol.com
writes:
> I use grade 5 when replacing grade 5 and sometimes when replacing hardware
> grade bolts. Using grade 8 can cause some problems because grade 8 is more
> brittle. It should only be used where it is needed.
>
We have had quite a discussion about this on several occasions on the list.
Generally I agree with Alan, but there is a consideration that makes me think
replacing with Grade 8 is sound. While the Grade 8 is more brittle, as in
not as flexible and "stretchy" as the Grade 5, the brittleness does not
become a factor until well after the grade 5 bolt has stretched and groaned
and broken. For instance, a Grade 5- 7/16" Fine thread bolt has a proof load
of 10,100 lbs. and a tensile strength of 14, 240 lb. A Grade 8-7/16" Fine
thread bolt has a proof load of 14,250 lb.(equal to the TENSILE strength of
the Grade 5) and a Tensile strength of 17,800 lb. So while the Grade 5
fastener is stretching to its tensile strength of 14,240 lb. the Grade 8 is
just getting started.
There IS a happy compromise: The Bowmalloy bolt, produced by Bowman,
headquartered in Cleveland (1-800-726-9626). The Bowmalloy 7/16" Fine thread
bolt has a proof load of 18,520 lb and a Tensile strength of 21, 370 lb. No
financial interest, and I have never used the Bowmalloy, but I have seen it
demonstrated and it ranks well above a standard Grade 5 or 8. I am NOT an
engineer, just know what I saw. The engineers on the list may be able to add
something to this.
Stainless is out of the question unless it is not a load bearing bolt.
Holding wings on, etc., they are great.
--David C.
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