Originally Posted by Pocko

Excellent question arid!

I have often thought about this myself, but it's one of those things that one thinks of but never dares to pop the question and risk being seen as the village idiot who challenged the status quo. Too late now, looks like you and I are out of the closet.

The logic of right-hand and left-hand threads actually makes perfect sense to me when I contemplate on the rotational orientation of pedal spindles. However, the opposite seem to be true when the principle is applied to the bottom bracket axle. If anything else, the forward rotation of the axle would be in the same direction that would loosen the bearing race threaded to the BB shell.

I have often wondered if someone had made a mistake back in the early days, but by the time it was discovered, it had been already too far entrenched in manufacturing standards in order to be rectified (speculation). The first time I built a frame with a threaded BB shell got me worried that I could get the BB round the wrong way if I wasn't careful. In fact, because I was determined NOT to make this mistake was when I first realized this possible anomaly. I was so concerned that I checked, double checked, and triple checked this... and was really surprised by the threading orientation. It was the opposite of what I expected.

Perhaps someone here could give us the official (or historical) reason for this... I certainly would also like to know.

Takers anyone?