cossy abuser,

Why do you think I have something against you?

Regards reusing stretch bolts, I'm affraid its a BIG no. This is'nt to say you can't reuse them, its just unwise to as you have no idea how far off its yield point the bolt is.

The technical reason for this is because all materials have an elastic region within the ultimate tensile strength, and then you enter the yield area where permanent deformation, and hence ultimately strength rapidly falls.

A stretch bolt by definition, is elongated during the torqing process so that the bolt remains within its elastic region. This is the region where by the tensile strength has not yet started to fail through bolt elongation.

By reusing a stretch bolt, you may well still remain within this elastic region, but eventually you will elongate the bolt to the point it reaches its yield limit with failure occuring soon after!

If you need to see this in practice, look into how material is tested for its tensile strength. You'll find that most metals are tested using a test piece representing a known diameter rod, and after XX% extension the metal yields and fails, a little bit like stretching an elastic band far too much. unfortunetly for metals the amount of elongation allowable before yield is'nt much as a percentage, hence why grinding the bottom off your head bolts to allow them to stretch further is a BAD idea.

Hope that helps,