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Originally Posted by The_Beast
They are 1/4 inch diameter, meaning you would drill a 1/4 inch hole to put them through with metric threads, actually you would drill a 15/64 (5.95 mm) hole to drop them through.
If you really want to be an arse and get that technical they are 1/4-28 with an NF-UNF pitch and you use drill no. 3 decimal .2130 mm 5.45 this is the thread size and diameters you use to drill and tap a hole to put them in.
Now do like everyone else and just go and get any 1/4 or 15/64 coarse thread bolt of your choice and stick in the hole it will rethread the hole itself since it is only thin sheet metal and be done with it.
Ford has actually switched back and forth between coarse thread 7/32 (5.56 mm) diameter screws and the others I gave the dimensions on above. You don't have to have an exact thread size and pitch as long as the diameteris bigger than the hole diameter it will go in and thread itself.
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ah, so it appears to simply be a misunderstanding in nomenclature. But, since you want to get technical, we can get technical.
NF ≡ American National Fine. The American National Thread took the US standard sharp V thread and flattened the crests and roots, thereby strengthening the thread.
UNF ≡ Unified Fine. The Unified thread was adopted by the United States, Great Britain, and Canada during World War II. This thread adopted the 60° thread angle of the US (Britain had been using the Whitworth Standard thread with a 55° thread angle) and created a rounded root, with a flattened or rounded crest.
So, calling it a NF/UNF thread is somewhat redundant and
technically incorrect. Although most taps are sold as NF/UNF taps.
And now to your "metric thread". A Metric Thread has the same 60° thread angle as the UNF thread. But a Metric thread has a flat root and a flat crest. (remember, the UNF has a rounded root). So it is impossible to have a UNF Metric thread -
by definition they are different designs.
Thread size is defined by the nominal diameter. This diameter is defined in either Inches or Millimeters. So theoretically you could call a 1/4" bolt a 6.35mm bolt (since .25*25.4=6.35) but you'd have trouble buying a 6.35mm bolt.
and for tap holes - yes, a 1/4" UNF tap hole size is made with a number 3 drill. This correlates to a diameter of 0.2130 inches. (okey dokey, lets convert that to metric... 5.4102 mm... but its still not a metric thread)
ok, enough ranting. I just get somewhat annoyed when someone mis-speaks and then restates their mistake as fact. Its especially annoying when they try to insult me in the process.
Thanks letting us know its a 1/4" fine thread (or maybe coarse...). Based on the detail of your reply I can trust your knowledge that they are indeed 1/4" bolts. Now I can search for some black oxide screws to replace my rusting ones.
- drilled 3/16 re-tapped american style - Stainless bolts are a must - Medium Course w/anti seize..
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