The "B" Nut can be Deadly

Maintenance Safety Tip
Notice Number: NOTC4301
The "B" Nut can be Deadly
All aircraft maintainers have heard or used the term "B" nut.  It is the common description of the nut that is used to connect fluid lines and hoses. It is a very simple component; but does a critical job. It provides a reliable seal in plumbing systems and usually results in ease of maintenance for AMTs. It is designed to provide years of reliable service. However, "B" nut reliability is only as good as how you treat it.
We disconnect and connect them many times during our careers - right? However, do you "tighten" or "torque" this simple critical component? No matter how simple this component is, it requires a specific "torque" to keep it reliable in maintaining plumbing system integrity.  You may have seen a maintenance record entry where the sign-off stated, "Tightened B nut."  Does this mean it was tightened enough to stop a leak, or was it tightened to a specific torque? If you are just tightening the "B" nut, you could be setting the stage for future failure or fracture.
Just get the tools you need to get it done right!
Another "gotcha" is finger tightening then "forgetting" to torque the "B" nut. A high risk of this occurring can be distractions (like telephone calls) and interruptions (like multi-tasking) while on the job.
A good technique to follow is if you connect a "B" nut, finish the job with the proper torque. Otherwise, tag it or write it up so it is not overlooked, especially if you leave the job site or another AMT finishes the job!
Over 10,150 AMTs earned an AMT Award last year. Will you, this year?


Also if you can’t run the “B” nut all the way down with your fingers something is wrong.

Careful of over tightening a B-Nut and thus stripping it. Many components, hydraulic lines, B-nuts are located in difficult areas and many times you need to tighten them without seeing them. Checking for leaks can be difficult. Try to use a mirror for inspection rather than feeling by hand, However one note of caution, is not to over tighten. If you strip it you may end up having to remove structures or components to extract the line and make the repair or get a replacement, all of which will be costly, especially if the plane goes down for maintenance. Surprisingly, its not that hard to overtightened and strip it. Be careful. If you can, make many practice tightening in the shop environment to get a feel for the range.

Also. Never feel for a leak, they can only remove the tissue, not the injected fluid. If you can’t run the “B” nut all the way off with your fingers (after torque break) something is wrong. If you can’t break the “B” nut torque with a standard wrench be suspicious. If you find a seep ALWAYS loosen FIRST then retorque. If you find a leak take it apart and find out why. If someone asks you for some “red stuff” restrain them with duct-tape and find out if they worked on the acft before you did. 