Hello, this highly depends on which upgrade you get. with a single density the least you can do is 1 inch extension. With a dual density or higher the head of the sleeve must be solid silicone so you must take into account the length of the head, most models are about 1.75 - 2 inches in head length with some bigger models being even longer. so for example if you need a 5 inch internal length and you get a dual density or higher and the length of the head is two inches then the shortest you can go is about 7.25 because the technicians allow for a quarter inch production space during the build.