I ordered these lock cylinders because I have two entry doors that were keyed differently, but either key would operate both deadbolts. Then I learned about the master key policy. The cylinders marked with an M, should be on the paddle handle, can be opened with one of four master keys. This is done so the dealers can access your R.V. without having to carry a huge ring of keys. I don’t like the idea. Anyway, I wanted to have both entry door keyed alike and without the Master cylinders. They fit perfectly and are easy to change. They say you need a change key to replace the cylinders but you really don’t need that. If you put the lock in the open position and insert a thin stiff wire, or a lock pick, into the key hole, all the way into the lock, and lightly the rock the tool in the slot the cylinder will come right out. To reinstall place the new cylinder on the new key, make sure the lock internal is in the correct position and insert the cylinder back into the hole. Look on YouTube for videos. Amazon had the best prices on these cylinders.