There have been several posts here about bolts or the threaded area on bolts failing so, just for the heck of it, I did a couple of "look ups" and got surprised (this is not the first search I got, the one that startled me).
https://www.bing.com/search?q=cut+threa ... f2b5daeaa8
When I started working in engineering (back in the mid-1960s), I did draw up several bolt patterns, for the company I worked for, some of which later became Mil-Standards. As part of drawing the patterns up I also had to listen to the engineers and the specialist engineers surrounding my desk talking about fastener design and what I needed to have on the drawings. Cut vs. rolled threads and what I would need to know about the difference specs on making and materials used in different strengths of bolts ("grades"), very complicated discussions for a beginner.
If you look at the drawings of the two different types of threads shown in the URL and the grain direction shown in the bolt of each style of threads, the drawings don't necessarily agree with how the grain of the fastener looks. Part of the drawings (mil specs here) includes how the grain of the bolt (the shank in this case) are formed to run in the direction of the length of the shank not helter-skelter. The rolled thread grain direction is compressed towards the center of the fastener, but the grain is not removed as in the cut threads.
Again, the "cut threads" dig down to the spec depth cutting away material while rolled threads compress the material making the rolled threads stronger (I've shortened the discussion due to giving out information that is not to be shared ).
In reading one search (not the one shown here) there was a statement that the rolled threads can have a larger diameter in the threaded part. If that is really true, that would indicate that the rolled threads are not fully made (according to mil specs in this case) which could be the reason some of the bolts are failing in the threaded part of the bolt (threads are not really designed to handle "shear loading" as is the non-threaded part of the shank (aka the "grip" or some other terms for the same unthreaded area that are used).
If what I read, in another URL discussion on the web, about the difference between cut and rolled threads and the stated expansion of the dia. of the threaded area in a rolled thread could be the reason for some bolt failure especially in the threaded part of the fastener may be there.
Recently I tried to get some information on some specialty bolts I had bought but what little info I got was sketchy but then I guess they don't give out secrets like Mil-spec bolts don't either I guess.
This discussion is for what it is worth.
Lee
Threads on bolts
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Re: Threads on bolts
https://www.aftfasteners.com/grades-of- ... gth-chart/
Some additional information on fasteners, for what it is worth, but it doesn't give the cycle limitations of the specific fastener. It does not give the cycle limitation of the fastener. This is the number of times the fastener can be torqued to its limitation then removed.
When the fastener meets this cycle limitation, it probably/conceivably/potentially starts to weaken (stretch/fail).
Lee
Some additional information on fasteners, for what it is worth, but it doesn't give the cycle limitations of the specific fastener. It does not give the cycle limitation of the fastener. This is the number of times the fastener can be torqued to its limitation then removed.
When the fastener meets this cycle limitation, it probably/conceivably/potentially starts to weaken (stretch/fail).
Lee