A few people can do it. I would love to be able to do it myself then no more brakes ever again. 16t and 13t are both different threads. The side that hasn't got the 16t freewheel on will take the 13t freewheel. Provided you did buy the flip flop version and not the left and right hand version. So you haven't wasted your money. If you still get some trouble then post up a pic of the threaded sides, (side on pic) then i will be able to tell you what you have got. Some interesting news (perhaps) Not being a fan of Primo powerbite cranks because of the insert, Primo have made me and friends turn our heads back towards these cranks. Now with a hexagonal shape insert, the insert shouldn't spin like before. There in the issue of ride. I don't acutally own just saw the pic.