Bizarre Nuts

[Target9000]

So the other day I was in the anchor locker removing the stemfitting of our boat. The nuts that held the bolts there were very hard to remove. I ended up grabbing them with vice grips while unscrewing the bolts on the outside of the hull.

Interestingly enough, the bolts themselves were 9/16" but the nuts that were on the bolts were very much larger, almost 3/4". However that isn't what the bizarre part was.

They appeared to be sleeved. One of these nuts actually broke in half while the sleeve inside it was still in tact. I've seen helicoils and such used in engine blocks, but never anything like this. For the life of me I cannot figure out what was going on here. Anyone got any input on why the heck this was done?

[Cheechako]

Strange indeed.

[Outwest34au]

Rivnuts in bigger nuts?

[Blue Stocking]

57 yrs ago, as a10 yr old, I used to hang around a Goodyear tyre shop picking up hustles on detailing cars and trucks--and helping the big guys change truck wheels.
English Commer trucks had deep wheel stud nuts that went on initially with a deep socket, air impact wrench. You then backed the socket off the nut to the outermost flats, and torqued an extra 10 lbs. This "wrung" the nut tube, and acted like a jam nut. New nuts every change. Nuts looked like those.