I used a hose clamp when I was doing it. Worked good for me. I got somewhere between 3/8 and 1/2 inch permanent girth in about 3 months.
Looks like this: I’m sure you’ve seen them before. You probably have a couple in the bottom of your tool box. I customized mine by grinding the edge of a small coin flat, then silver soldering it into the screw slot so you can tighten and loosen it just with your fingers.
Wrap your penis underneath pretty thick with a good soft fabric or something. Slide the clamp to the base of your penis and slowly tighten it while you kegel blood in. You’ll know when you’re tight enough, when you’re remaining bulging swollen without having to keep kegeling. Don’t tighten it any further than you absolutely have to. Leave it on for 2 minutes when you start. A week later maybe, you can move up to 5 minutes, maybe 10 once you get used to that. It’s easiest if you get partially erect first.
Just be a little bit careful, and don’t do anything to the point it hurts. Start easy, maybe even wear it a little loose the first few times. Work your way up from there until you get a feel for it. One more thing, some are smoother inside than others. Run your finger inside it to make sure there are no sharp edges or little things sticking out. Pick a good smooth one at the store before you buy it.