For primaries, it seems like only one side is usable--the other is too thin. for secondaries, I think you can use both sides, as both sides are about equal in size. keep in mind that a feather has curve in three dimensions, so for any given arrow, all the fletches have to match. That is, if you decide to use the "off side" of a left wing secondary feather, then all three fletches should be "off side" secondaries from the left wing. Then mount them on the shaft so that the feathers create a rotational force on your arrow so it will spin. I have used both sides, but I am not a great shot, so it is hard for me to say if an arrow shoots bad because of a fletch, or because I have a horrible release. Someone else with more experience can perhaps chime in.