I have the 4", 4 3/8", 5.5" & 6" The 5.5" came with the machine, the 4 3/8" is made by Flex I believe and the other two are the LC interchangeable kit. They all work just fine. Just make sure you use the flat washer when attaching a different bp and the allen head from the Flex and LC are unfortunately different sizes. Believe one is 5mm and the other 5.5mm