I have big balls and a small cock, so I tried cb6000, holy trainer, a metal one with wire tube, so long as they had the large rings, They technically fit, but all of them mashed my balls with the tube. I finally tried a nub and bam, PERFECT fit, and I used to fill the cb6000 when I started 10 or 11 years ago, but now I can just push it inside myself, put on the nub, and my little guy just pops right in. I cant urinate in it though, but it's easy to unlock and remove the nub, do business, re-lock is easy and doesn't pinch (unless you are hard or semi). I can't recommend a nub cage enough 🙂