What kinda high strength steel would that be there Roy? I bet they are just made out of plain ole steel myself,,it won't create any stress risers as long as you get a decent weld on it,,probably all thats needed is a good size tack,,I'd rather weld on something like that to attach a little light bracket than drill a hole,,now theres a stress riser for sure. [edit here,,,after thinking about that word high strength steel,,lets assume it is,,,that don't mean you can't weld on it,,,thats just a word which can mean alot or very little when it comes to welding,,all kinds of high strength steel, different grades,,main reason it would be used on roll bar would be it would be lighter weight than a piece of mild steel that had same strength,made so by alloy,and or a heat treat of some kind,most thinner high strength steels,can be welded with 6011 or 6010 rod even with little or no preheat,,let alone post heat,,some can't,,but if this roll bar is that hard it would be to brittle to use as a roll bar,,and we are talking about a few little fillit welds here probably,,if you wanted to play it real safe,preheat it to 150 degrees and use 7018 or 70S mig wire on it ,and keep welding to minimum, and again assuming that the weld would be neat without undercut,,,]thingy