"Bob La Londe" wrote in message ...

I just checked. 1/4-32 is a standard for UNEF.

UNF is indeed 28 and UNC is 20 though.

I often forget to check for UNEF threads until confronted by one.
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Here are some other odd threads you may encounter:

https://www.buyfittingsonline.com/pa...ifference.html
NPS shows up in shower spray hoses that seal with a rubber washer, and
hydraulic "swivel" fittings.
https://www.discounthydraulichose.co...vels-npsm.html

https://paxtonhardware.com/blogs/news/lamp-thread-sizes
It's another untapered version of a pipe thread.