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Found a supplier, Aetna Screw Products. "The unique head design accounts for the superior performance of The Aetna 6 Slot GM* Type AA Hex Head Place Bolt GR.8. There are six slots on the top, a recessed center, and an undercut at the base of the head that meets the shoulder. This design...

Turns out that the locking action is in fact in the head design of the bolt. One patent that is the basis for the bolt used on the xm757 is #2,543,705 (see images below). Ford had hoped that this series of vehicles would be adopted by the army and wasn't afraid to innovate, parts that no longer...

Jason, I think you are getting warm, my best conclusion, so far is that the bolts are "close tolerance" types and the self locking action is tension, the same as found in cylinder head bolts, machine tools and examples you listed.

I like the "detective" work, besides we learn a lot from asking these kind of questions. A lot of my posts and articles come from digging deeper, some of it has become "common knowledge" on this site as a result. Anyhow, I went to the source, at least I was hoping I did and this was the...

Thanks for all you replies, much appreciated. I don't want to substitute the specified bolt, MS35764-669, but would like to know by what action it locks. The safety wire would only be to keep them from turning more than a fraction and not fall out and yes the bolts would have to be torqued...

Gottcha Dan, but I would like to know what I have on hand, this truck (xm757) has shown me more than one unusual solution to old problems. A little hard to scan, but here is a side view. The underside is flat except for an annular grove, which makes me think that there is some flex involved to...

What's currently used, any problems with them?

That is really what my intent is, but I have no source for new ones and as stated in the first post, I don't know what feature of the bolt provides the locking action and they thread easily in and out of the tapped hole....unless there is something about the head design (flexing?). The safety...

Ferrari does it. :-)

Safety wiring will at least keep the bolts from turning more than a fraction of a turn, it won't actually "lock" the bolt in place. The fan blade bolts on the xm757 engine are safety wired, no doubt, to keep the bolts from go flying if they come loose... Another observation, with the wire in...

Scary thought, I will replace all of them for sure, what do you think of safety wired bolts? BTW, I checked the TM specifically for the "throw away" instruction, but there was none for this part....(NSN 5306-00-071-4473)

After reading the thread by Russ and his drive shaft "incident", I started to look at the xm757 and it uses self locking bolts as shown in the images below. My question is, what part or feature of the bolt makes it "self locking"? It screws easily all the way in and uses apparently ordinary...