Good question! I re-read the various standards (at least as described by
Wikipedia) and combined with the Alpine parts reference cited earlier I don't
think that these are British thread after all.
BSW (British Standard Whitworth) in 1/2" has a 12 thread pitch, while BSF has
16 threads per inch. We know that the chassis bolts are 1/2-20. UNF is spec'ed
at 1/2-20 while UNC is 1/2-13.
So the question that remains is, are these bolts made with a 60 degree thread
profile or not? If they are, are they designed for an interference fit (which
might explain why a standard die will remove material from the bolt threads)?
As already stated, these bolts have a longer threaded section and shorter grip
length (thanks Mayf!) than a standard SAE bolt, so you can't easily go to your
local ACE hardware store to buy replacements. Using a thread die to put extra
threads on a store bought bolt is dangerous because it causes stress risers at
the root of the threads - conventional bolts have the threads rolled into
them, which essentially forges the threads into the bolt and strengthens the
threaded area.
Theo
________________________________________
From: tigers-bounces@autox.team.net [tigers-bounces@autox.team.net] On Behalf
Of Carmods@aol.com [Carmods@aol.com]
Sent: Tuesday, July 13, 2010 3:07 PM
To: tigers@autox.team.net
Subject: [Tigers] Crossmember Installation Headache
Jul 13, 2010 09:52:38 AM, Theo.Smit@dynastream.com wrote:
they're British fine thread which is almost but not quite the same as SAE:
Theo,
Are you sure those bolts are British Standard Fine Thread (BSF)?
What size are they?
John Logan
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