This is the Gen 3 Oura smart ring, in size 10. It's the "Heritage" model, which is the one with the slightly flattened top and comes in Stealth Black, which is the (slightly more expensive) matte scratch-resistant finish. This is sold as "parts only or not working" because there is a fault with the battery. It's supposed to last around a week, but this one will only track around two nights' of sleep between charges, and that's with no activity tracking. It might be a good entry point for someone interested in the oura ecosystem, or someone who's only interested in the sleep tracking capability and doesn't mind charging daily. Physical condition: fine, with some light scratching in some places (pictured as best I can). Comes in the retail box with all the bits.
eBay