Jerry Moos contends
> I know for a fact that
> at least some of the SunTour expander bolts were in fact
> left-hand thread. This is from bitter experience as I ruined
> a set of SunTour barcons trying to remove them while not
> realizing they were left-hand.
I have only worked on a few hundred sets of Suntour bar-cons, certainly not all of them ever made, but they were all right hand threads. Most people think they are left-hand because you turn them clockwise to loosen. But this is because the "head" of the bolt is in back, behind the three-part expander plug inside the handlebar. Turning a right-hand thread clockwise makes it move away from you. If the head is on the backside of the work piece, then that is loosening.
Try it with any normal bolt and you'll see what I mean. Of course, you can't normally wrench on the "tail" of a bolt, but imagine that it is hollow and broached for an allen wrench. Also fiddling with a bar-con with it out of the handlebar will usually convince you it is a right-hand thread.
Jerry, if you had to turn the wrench counter-clockwise to remove the bar-con, then it was left hand thread. But as you asked, why would they do that?
Seattle WA USA