Frank,
Just gently roll the shafts on a smooth surface like a kitchen counter. You will easily notice their stiff side if they have one, when they begin to stop rolling they rock back and forth with the stiff side down.
Then, mark the stiff side with a piece of chalk, and roll them again several times. 9 times out of 10 rolls and mine always landed chalk marked side down.
I had the luxury of rolling mine on a large 36" mirror we had taken down from a bathroom remodeling job. Just make sure your surface is flat.
Another way I was told was to plug both ends of the shafts and put them in the bathtub, they will float stiff side down.
I shoot mine stiff side agains the riser.
Hope this helps,
John