Sizing yourself properly for a CB device of any kind, even a relatively simple "trapped-ball" design, is a somewhat counter-intuitive process. If you just lay your shaft on a ruler to get a cage length measurement and wrap a string around the base of your scrotum to get a base ring measurement, I can *guarantee* that many, if not most of you, will have the wrong measurements. If you send those measurments off to a custom CB device maker, you're probably going to find the base ring is too tight to sleep in, and the cage is longer/larger than you would like. Have I piqued your interest yet? I have a system for taking your measurements that should yield perfect results for your base ring, cage length, and inside diameter of the cage on the first try from your custom-fit device builder. The only thing that's really hard to measure for is the "gap" between the cage and base ring, but fortunately that is a very easy and inexpensive thing to adjust for most custom-fit device builders if need be. First, some observations about typical sizing misconceptions Misconception 1: If your device slips down your shaft/scrotum too far, your base ring is too large. Misconception 2: If you can "pull out" your shaft from the back end of the device, your base ring is too large. Misconception 3: It's normal to feel "night pain" while sleeping. It's normal for your CB device to wake you up. Just go pee and that will let you get back to sleep. Just put some lotion or oil around the base ring at night and it won't be so bad. It's normal to get some sores at first, or every now and again even after being in chastity for a long time. Just give it a few weeks/months and your body will adjust. Use some lotion or ointment when the sores crop up; they won't last long. Misconception 4: You need a cage whose inside diameter grips your shaft fairly tight. It's normal to require a lot of lube or "the stocking trick" to actually pull your shaft all they way into the cage. Misconception 5: You need a cage that is *long* enough to give you a little "room to grow". Misconception 6: It is possible to design a trapped ball cage that is "inescapable" without locking a piercing to the end of the cage or without a *deep* (and therefore dangerous) urethral insertion pin. The following posts will elaborate on these misconceptions, and then will detail my sizing system. If you need any further incentive, this sizing system gave me a perfect fit for my Jailbird from Mature Metal on the first try. This is 100% comfortable for full-time 24/7/365 wear with zero night pain.