First off, buy the next smaller than you feel like you need. Especially smaller than what you actually measure according to the provided sizing guide. I bought the 45mm & 50mm. Both work fine for me. 45MM is pretty tight on me, but feels good. 50 is good for non-sexual everyday use. But I might be unusual, my balls are like a teens balls, don’t sag down at all. They are tight up against me, so my thickness is large around my base and balls. I feel like most men’s sag more which just leaves the thickness of your shaft basically, so wouldn’t need as large of ring.
Feels good on, and once in a while if it’s not worn pulled up tight to my base, my right nut will slip back out towards me.
Best ring though I’ve worn so far.

Using a flexible tape measure, when it's really tight, I measured 4.75 inches. When snug, 5 inches. All measured when I was soft.

40mm fits me great. Even when hard, I can get 2 fingers under the ring, and a third finger if I try.

I don't use the ring for ED issues. I use it to keep my boys front and center. And it works great for this purpose.

It's comfortable, and since it's not tight fitting, I've worn it for half a day with no ill side affects. All day would be fine too.

Happy with my purchase.

I got the Power Flex 50mm and 45mm put the 50mm on and it is super comfortable love it so far since I’ve been looking for a cock ring for a while now and hadn’t found one but this one so far has met my expectations can’t feel it’s there and I love that since I plan to wear it 24/7. Only one thing I’ve been thinking that I’m a big grower and my balls are tight very often and don’t know how the thickness is going of the ring going to make that a problem don't know if the thinner version would fit better haven’t tried the 45mm yet want to wear this one for a day or two so I can get used to it being there will update when I try the smaller one on

Uniquely shaped silicone cock ring. Totally awesome erections and orgasms. Now thinking about a smaller ring for longer erections.

I have quite a collection of c-rings and the Power Flex is immediately my favorite. Amazingly good fit (taking the advice to go smaller if you're close to being between sizes) and so comfortably smooth. The key shape allows full force, unconstricted, orgasm.