Whitworth & UNC thread forms

[Eric The Viking]

I haven't got a Zeus guide, but my "Presto Counsellor" says the pitches of 1/4" and 3/8" UNC are the same as their Whitworth equivalents (20 & 16 TPI respectively).

I want to repair some stripped threads on audio gear, and UNC Helicoil kits on eBay are cheaper than Whitworth (and easier to find), so I was wondering if the threads are identical, 'close enough' or 'wildly different'.

I'm guessing 'close enough', given that UNC derives ultimately from Mr. Whitworth's work, but thought I ought to ask the team before doing anything silly (like buying anything!).

Comments welcome.

E.

PS: Just used Wikipedia: Whitworth has a basic form of 55 degrees and UNC is 60 (if I understood it properly!). Will the difference matter? It's only holding microphones on stands, etc...

 

[wizard]

yes they are the same

 

[Eric The Viking]

Brill, many thanks!

 

[CHJ]

..PS: Just used Wikipedia: Whitworth has a basic form of 55 degrees and UNC is 60 (if I understood it properly!). Will the difference matter? It's only holding microphones on stands, etc...

Like camera mounting threads (Whit-Metric) there are some maybe's. often depends upon which way round the mix is (Male-Female) as to whether they will be a loose fit but clamp up securely or a binding fit that works, so many variables on quality of the threads in the first place etc.

There's between 3 and 10 thou. difference in core diameters and finished thread form in the 3/8" versions in various areas although both use a 5/16" tapping drill for common usage..

 

[Wildman]

as the helicoil inserts will come with a tap fitting the insert is ok. screwing a whit male into a UNC female will only present a slack (because of thread angle) fit.

 

[Eric The Viking]

Thanks chaps. I'll buy a UNC kit and try it in something scrap, but that's probably being over-cautious. Wildman confirms what I thought. The other way round it might, just, pinch, but it'll be the loose-fit way, which is fine.

As with normal Helicoil use in white metal, the 'fix' will likely be stronger than the original.

Thanks,

E.