I'd say they are not as often used, but certainly are available.
What I haven't found is any in stainless steel like I have most all the other sizes in.

Seems a little odd that 7/16-20 tube nut is hard to find, when that is a normal fine thread for 7/16 bolt.
The extra fine thread 7/16-24 which I would think is more unusual is in fact easy to find and common on tube nuts. Not a perfect comparison, one is a bolt and other a tube nut, but odd none the less.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-