Crash bars installation query

[R65North]

Hey Guys,

I have fitted a pair of nice used crash bars today. Another 'simple' job that took a morning! I had a couple of questions about the 'U' clamps that attach to the frame.

Is the purpose to tighten the clamps until the crash bar tube contacts the bike frame?

How tight should the clamps be? It seems there is no 'tightening' point but I don't want to damage anything, particularly the frame.

Thanks for any shared experience  

Cheers
Dave