The B-Nut

The B-Nut is used on AN fittings.

I learned early on in my career that it was called a B-Nut, but where that name came from, I never knew. I have, however, found a reasonable explanation on the interwebs at this website. In case that link ever goes dead, I shall copy its text herein...

Now for those who work on aircraft, you will recognise the B nut shown above. Well a B nut is a nut at the end of an aircraft tubing that connects two tubes or connects a tube to a component.

I had been for a long time wondering why it is called a B nut. There is no A nut or C nut. Googling it didn't help. I only found out there were others asking the same question.

Lately I discovered an article entitled "B-nuts" and it was about B-nut maintenance and covers how to properly tighten a B-nut, how to tackle leaks at B-nuts etc. The article starts off as follows and until there is another explanation, I will go with this.

{Why the "B" in B-nuts? Most technicians are familiar with the AN standards nut which is commonly referred to as the B-nut. But do you know where the "B' came from? About two generations ago when our forefathers were flying around in open cockpit planes, a sleeveless coupling nut was used in connecting the airplane's copper tubing. However, this nut would often gall or twist the flared end of the tubing when it was tightened. In order to reduce the wear and tear on the tubing, a protective sleeve was added. To distinguish between the two coupling nuts, the mechanics began referring to the sleeved nut as the B-nut. Thus the "B " designation came into existence where there had never been an A-nut. }

Unfortunately I cannot credit the writer of the article or even the magazine because what I have is a tattered and torn photocopy of a single page from the source and on this page there is neither author nor magazine name.

The above comes from

Fitting: B-NUT
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