Originally Posted by kraftwerk
I noticed some are "flip-flop" but that does not mean anything either way..
Flip-flop hubs are designed to have a fixed cog/gear on one side and a one-speed freewheel on the other in case you'd rather coast. Only one side is threaded for a lockring, so you can't put a fixed gear on both sides without running the risk of having that gear come off sometime when you are slowing down.