I would bet its 13 keeps the ring on when you back the axel lock nut out if you dont have it on you will loose the ring and then the axel will come out.
the ridge holds the ring from expanding

 

I think you might be right. I tried it there but it did not look right and I thought the lock nut needed to go over the ring to keep it secure. Will retry it again with 13(my extra washer) between 16 and 12.

That has to be how it goes.

Thanks pipelayer

 

no problem I dident want to see you loose your axel