[andrew15]

Well, the problem with checking to see if they are stretched or not is that you need the baseline figure from when they were installed. I'm pretty sure you measure the length of the bolt, record it, and then install the bolt to the proper stretch. At a later date when you dissassemble, you compare the current bolt length to the previous recorded length and if they are within a particular value, they are fine to reuse.

Basically, if you don't know what the base length was prior to install, get new bolts as they could have been over stretched during the initial install.

Regards,
Andrew M