Originally Posted by tracy
Steve, can you give the part number for these nuts? Thanks
As shown in the original post where we did the strength tests, the bad nuts are NAS679A6. The good nuts are NAS1804-6.
The origin and history of the NAS679 nuts I believes goes back to the development of rockets. They have ring flanges that hold things together that have many many bolts and nuts around the circumference of the rocket. There was a desire/need for extremely light-weight nuts to save weight because they had hundreds of them, so these stamp-formed nuts were developed. Considering how they are made and now little metal is in them, they are pretty strong. But they are NOT appropriate for high-load bolted joints such as our landing gear attachment.
The band of metal that surrounds the bolt threads, which has the nut threads on the inside, is so thin that when you pull, the band expands because of the outward pressure from the thread acting like a wedge. You can watch as it expands enough to climb over the thread, then shrink back down again, having climbed one thread up the bolt.