So after some careful measurement, I've found I am directly in between 40 and 45 ring diameter. I just did a test using cable ties and found 130mm circumference to be possible circulation poor, 145mm circumference to be somewhat too easily escapable, and the range 135-140 just about right. Given the choice, I think the 45 is the proper size for me, as it can always be clamped down a little bit more, right? Is there enough give to avoid pinching? BTW, I can get both balls and penis through a 115mm inner diameter solid brass ring with no issues while flaccid. Getting aroused while in this was anything but pleasant. That is far too small (would be a 36 size birdlocked), but suggests a disturbing trend - I can easily enter and exit a size which impinges greatly on circulation. I hope a trapped ball device can actually work for me, maybe the extra width of the ring will cause the skin to be stretched and make escape impossible, but I suppose I have to find out for myself. If it's escapable, I'll eventually fix that with a piercing, likely a frenum. About the diameter, any words of advice? Based on feedback, I'm ordering a device either tonight or tomorrow, can't wait any longer. I need to be locked up, sooon, can't take it any longer.