Hi,

Interesting statement you made.
“ As I understand it, the reason not to reuse "single use bolts" is that you can only reach the correct fastening torque once.”

I would say it “As I see it.”
I’m not sure where or whom came up with single use bolts to begin with, except NASA!
They are or were working with almost an unlimited budget, back during the “race” to the moon!
I know I’m a result of some of that industry from time to time!

My budget and mostly anyone else’s in our lifetime race events, do have a budget!
That is except with the printing machines of our own Treasury!
These notes, that hold the country together, are being over torqued in ridiculous amounts!
The people in our country have been weaken, in this germ “war” and the “fare” of the past year! It’s attacking our American belief in common senses!

With that said, a lot of their stuff went only one way to space or into an ocean, so that makes them a one time use fasteners!
You are correct in that a bolt gets stretched and there are yield points of the material to be mindful of.
This is why we make instruments to show us these limits.
One is our torque wrenching methods.
Now the number of times a material can be taken up to its limit or past, is up to testing it and certifying that material. This is the result of learning how far you can push “things!”

On brake calipers versus engine head bolts are two completely different applications!
On engine heads, you have repetitive vibrations from combustion and the heating and cooling associated with all that!
Brake calipers are subject to heat and cooling but no where near that of engine head bolts!
Common sense says, the forces are lateral to the bolts diameter and not in tension beyond the stretch set with a wrench.

Now guess what, you can use head bolts twice according to engine designers. They have built far more different engine designs than brake calipers but engineers learn and watch each other all the time to keep their jobs.
There become a respect value but not always earned if each doesn’t take the time to learn the details but will do things because it seems right.
The word “safety” runs in the back of their minds and “covering ones butt” runs in between the ears as well!
So with that, I will say that both an engineer and a technical writer has put forth the information in manuals to put the “monkey” on someone else’s back!

I don’t see that these bolts, used on the calipers, are having any special markings and I’ll bet do not have certificates supplied by the manufacturers. Grade nine, is like NASA stuff!
There are made but are exclusive to racing applications.
Not like “most” of out everyday “factory production” and boxed “as head bolts,” that are reused at least once.

Thread locker or snubbers started out as a “nylon pellet” placed in a hole made in the thread with an end mill. They were called one time use pellets along with “ Nyloc” brand nuts!
Before that, aircraft and other critical items, made by man, were hand wired through the head of the fastener, above the stress point of the neck, of course. The method is still used in some cases of extreme environments.

How many miles or years should head bolts last, on a Volvo? We are all working on that answer!
The worry with them is, “I don’t want to have to this again for a long time!”
It becomes, Not safety, but preservation! (:)

I have a box of those, set aside, but no “new”caliper bolts!

Phil