Originally Posted by
twobikes
If you are confused about whether something, like a pedal, is right hand or left hand thread; just think about whether friction from its natural rotation in use would tighten or loosen the threads. Designers always make machinery so bolts naturally tighten a bit in use. No one wants their stuff falling apart for no good reason.
Thinking about this "logically" will lead you to the wrong conclusion. For example, English drive-side bottom bracket cups loosen by turning clockwise and the drive-side crank and spindle also turn clockwise so you would conclude the cranking motion would loosen them. Obviously it doesn't.
What you have to realize is that while the crank is turning clockwise the bearing balls inside are rotating the opposite way and that motion tends to keep the cup tight.