Agree with the brands mentioned above. Having been on both sides, putting a guy in one and being in one myself, there is no one size fits all. Make sure you measure, and it helps to get one with different size rings. If you get one and have a little bit of a hard time getting into it, use a little lube. Start slow too, don’t expect to go full locked on day one, build yourself up to it. It’s also supposed to be uncomfortable but not outwardly painful, unless of course you get one with spikes 🙂. I locked myself this week with a cheap Ternence one from amazon and will probably switch out to my steelwerks classic soon.