"Brent" wrote in message
...

its an old trick so that when you load down a machine you actually
apply force to the fastener to tighten it. if it were threaded the
other way it would be gradually trying to loosen itself forever. IT
might never succeed but if it does it wont be a nice scene as the
bandaw konks out and possibly worse.

setting the thread backwards is a total prevention of that

Several years ago I did some work for a retired engineer. He showed me some
brass nuts and bolts that to this day are hard to believe. The nuts and
bolts were made one at a time and had a very special purpose. The bolt was
screwed in and out of a threaded hole to apply more or less pressure. The
bolt had to be adjusted periodically and had to be locked into position so
that it would not move. Naturally it had 2 jam nuts on it to tighten down
and prevent the bolt from turning until the 2 jam nuts were loosened. Not
too hard to imagine so far, right?
The problem with this set up is that there was only room for 1 wrench to
fit. Typically jam nuts need 2 wrenches working in opposite directions to
loosen or tighten. These "special" nuts and bolt worked differently. The 2
nuts loosened and moved away from each other on the bolt when turned in a
counter clockwise direction. When turned clockwise the nuts moved towards
each other. Think about that a while. ;~) The bolt had threads that were
both left hand and right hand. One nut was left hand threaded and the other
right hand threaded. The first nut had to be threaded and in position
before the second nut could be tightened against it because, they had to be
turned in opposite directions to thread them down the bolt. Weird.