If you get one that doesn’t fit or that you don’t like, there’s always the Sex Toy Happiness Promise (Edit: looks like bondage was added to the sex toy happiness promise only for purchases made between 11th November and 2nd December
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If you feel like doing some reading, the Lovehoney blog has a Chastity Devices Guide, and there are quite a few recent threads with questions and recommendations if you search cage - Which chastity cage?, Cages, Measuring for a chastity cage. If you’re not following this one already, these experts could probably answer any question you’ve got: