fine/coarse threads question

When do you use a fine thread? Why?
Afaict there is no real strength or accurate placement difference as long as
more than a few threads are mating.
Okay it's going to be a lot easier to tap a 22x1.5 mm hole in 3/4" stainless
than a 22x2.5 mm hole (I tried the latter earlier, I am still sweating and
there is now a spanner apparently welded at right angles to the tap), but
are there any other advantages/disadvantages?
Reply to
Peter Fairbrother
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Coarse threads are used in low-strength materials as they are less likely to pull out, and also less likely to jam when inserting, and quicker to manufacture.
Many engine makers used coarse threads on one end of a stud to go into alloy and fine for the steel holding down nuts.
Peter -- Peter A Forbes Prepair Ltd, Luton, UK
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Reply to
Prepair Ltd
I read that in the US the fine thread series, once known as SAE, was developed by the Society of Automotive Engineers because the shallower thread angle would reduce loosening due to vibration. It will also reduce the torque needed for a given fastener tension which is probably why they are used on cylinder head stud nuts. Fine threads are also used for improved fineness of adjustment and for adequate engagement in thin sections. In the US, at least, they seem to be used a lot less than before. Don Young
Reply to
Don Young

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