I am new to high-powered rocketry and want to learn everything I can about it before I start buying stuff. I've read "Modern High-Power Rocketry" cover to cover and curiously the quesiton I have was never mentioned. On Dr. Rockets casings (and others that use screw-in end closures I assume) the end closures are somewhat larger in diameter than the casing itself. I guess I have two or three questions. 1. Is the "38mm" on a 38mm motor for instance, the diameter of the case, the end closures, or the reload? 2. On some of the casings it looks like the head-end closure is larger than the casing but the nozzle-end one is not. How do you keep the motor in alignment with the airframe? I'm sure you could build some sort of adapter but as I've never seen anything of the sort mentioned I'm guessing I must be missing something. Any help would be appreciated.