I was looking at these
http://www.adameve.com/Sex-Toys/Cock-Ri ... -6399.aspx?
and thought about how the ones on the cock just look similar to plain old o-rings, so I went to an industrial supply place this morning and bought a couple of big o-rings.
One is 2.5" inside diameter and one 2.75" inside dia, both are 1/4" wide. The 2.5 fit the snuggest around my cock and balls, just tight enough when flaccid that there were no gaps but I could still easily slip a finger underneath. The sensation is like being softly gripped around my base.
Guys if you take your thumb and forefinger and make an "ok" sign, then turn your hand so that your palm is out, slide that down to the very base of your cock and also lightly grip around your balls, letting them hang through the circle. That's how it feels.
I've been wearing this one for 14.5 hours now and it has felt great the whole time, no discomfort at all. I'm going to step down the sizes and see how smaller ones feel. When it starts to get uncomfortable I'll go back up one size.
I do want to stress that I did NOT have an erection during the whole time. No way I'd wear one on an erection that long.
I did get a hard-on a few times to see how tight it would get. It didn't get as tight as I'd like while hard. I figure I'll need to have one for wearing during the day, like at work, and then one smaller, tighter one for jacking off. After I get used to this one I'm going to get one for the base of my shaft and also to go under my glans.