Posted By : Tim Willis, 23-Mar-2004,
08:44pm
Well nearly.......
A 5/16th UNF bolt will have a 1/2AF head, 3/8th UNF a 9/16th head, and 7/16th a 5/8th AF head, and the little one 1/4UNF has a 7/16th AF head.
You will also find UNC (Unified National Course) bolts on our cars sometimes, especially where bolting into aluminium, or the fixed end of a
stud.
UNC bolts usually use Whitworth head sizes just to add to the confusion.
You hardly ever need to pick up metric spanners or sockets on our cars unless they are replacement bolts, some replacement brake hoses, bleed
nipples, and pipe nuts.
AF covers 99% of all fittings.
Whitworth (or BSF) are used on UNC bolts as already mentioned and fuel pipe fittings.
Seems confusing, but there are slight differences which make the job difficult if all you have is a Metric set.
Tim
Willow Triumph
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Posted By : Martin Doe,
23-Mar-2004, 10:09pm
Just a few observations from a layman who has learnt the hard way.
One of the main differences is the angle that the thread is cut.Whitworth are 60 degree as are UNF and UNC but the "teeth per inch" is
different and the thread form is different i.e V form and U form.
Older American threads both coarse and fine are cut at 55 degree and metric is altogether different but probably more logical!
A helpful dodge is that some metric and BA threads are interchangeable on low stress applications,ideal for when you lose the teminal screw off
a switch or instrument gauge!
Also Whitworth spanner sizes are all on their own and I have yet to find a metric or A/F spanner that will fit any Whitworth hexagon.
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Posted By : Tim Everitt,
24-Mar-2004, 11:19am
I have found 'metrinch' spanners and sockets to be very tolerant of the various different bolt sizes. They seem to fit most, but not quite
all.