Hi, My regular device is a HolyTrainer v2 small, with their 36mm (weird shaped) ring. The device fits pretty much perfectly and is as comfortable as these things can be, I'm considering getting a jailbird because Mistress prefers the look of a metal device. I've tried a few cheap Chinese cages and while they work OK, they are less comfortable than the HT for extended wear. I tend to use 40-41mm rings - with the metal cages the size of ring seems to make a huge difference to overall comfort and usability. If anyone here have both JB and HTv2 small could they please share the measurements for ordering with MM? I'm assuming the oval rings would be more comfortable, and perhaps the double ring would be most similar to HT fir? Any suggestions welcome. -droog