Well... the story is that dead people in Thai are buried with odd numbers of amulets on their body (2,4,6,8 etc..) so people prefer, and came up with this even number thing.
But then again, Buddha no much pantang compared to Taoism. So, wearing how is up to you but i still prefer even numbers. One thing is the weight of weight 3 would be better balanced otherwise wear 2 wait the chain slant to on eside
