UNF; Unified Fine and UNC; Unified Coarse was established during
WWII to be compatible and interchangeable with SAE threads but there are
some slight differences between the threads. An SAE 1/2 -20 should go right
into those threads without using a tap. If there is a problem running the
bolt in from the bottom, run the bolt in from the top
Any time I put an SAE tap through a Unified thread I cut metal and
the UNF bolt feels a bit loose in those threads. An SAE thread chaser might
work OK but I have not tried. I prefer not to cut the original threads more
than necessary.
I prefer to cut grooves into the UNF bolt threads, making it it's
own tap and use it to clear Unified threads. If that is not possible I
would take an SAE 1/2-20 bolt and cut grooves into it to make a thread
chaser.
Yes, UNF taps are available but I have mostly seem them in kits not
individually.
My notes indicate that the crossmember bolt is 3 1/4" UNF, Auto S - thread
length = 1.7", shank length = 1.55"
Auto S is the bolt grade, I think S denotes about a grade 8 but I can't find
my sheet about that right now.
I have purchased many bolt from a Caterpillar dealer but I don't remember if
I purchased any crossmember bolts.
Ron Fraser
-----Original Message-----
From: tigers-bounces@autox.team.net [mailto:tigers-bounces@autox.team.net]
On Behalf Of Would U. Believe
Sent: Wednesday, July 14, 2010 7:19 PM
To: Smit, Theo; Carmods@aol.com; tigers@autox.team.net
Subject: Re: [Tigers] Crossmember Installation Headache
Here's a dumb question: Since these bolts are such oddballs in the US,
what's to stop people from using a 1/2-20 SAE tap and just installing new
Grade 8 SAE 1/2-20 bolts? Just curious. If that's an insane idea, is there
a source for suitable and appropriate replacement crossmember bolts
anywhere? Thanks. M
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