American thread sizes

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alan006

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I got a nice set of ex USA Navy taps and dies at a boat jumble recently. They are described as UNF and UNM. I know about UNF threads but have not come accross UNM threads before. An engineer I asked said he thought this stood for Unified Medium and was the size between UNF and UNC. He said that it was a size used by the Americans for aircraft fasteners.
Has anyone come accross UNM and is it a size used for the aircraft industry? I've had a quick look on the web but not found anything.
 
Just scanned through Machinery's Handbook, ie, a fairly comprehensive compendium of American workshop practice. There seems no mention of UNM, only C, F, and EF.
There is however a listing of Unified Miniature screw threads, but not abbreviated to UNM ; 0.3 to 1.4 mm dia.
Are your taps this small?
 
They are Unified Inch Screw Threads: UNC is coarse, UNM is miniature. You can also get UNF, fine, UNEF, extra fine and, strangely, NS which is miniature machine screw.
 
Thank you both very much for the info. The set is still all wrapped up in the original greaseproof paper but I'll have a look to see what sizes the UNM covers.
 
Sorry, that being, of course, the size of spanner needed for a particular bolt. 1/2" AF being a half inch across the flats of the spanner.
 
Threads

Hi I am most lightly wrong, but I think there was at some time in the past, a Motorcycle Thread, Could it be Unified Thread Motorcycle/ Just a thought
 
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