How do I size this ring?

Use the diameter and circumference chart: US 5 is about 15.7 mm across and US 13 about 22.3 mm. Because the band is wide, many people go up half a size from their usual slim-ring size. Measure a ring you already own across the inside.

Does the spinner actually spin well?

The band rotates freely on new rings, which is the point of the design. Grit or moisture in the channel can make it stiff, so keep it dry and avoid bending the ring.

Can it open bottle caps?

Yes, the edge has a notch shaped as a crown-cap opener. It works on standard caps but gives less leverage than a bar blade, so expect a firmer pull.

Will the steel rust or turn my finger green?

Stainless steel does not turn skin green the way plated brass does, and it resists rust. Prolonged contact with salt water or chlorine can still dull the finish.

It works as a low-stakes novelty gift for someone who fidgets or likes bar gadgets. It is not a substitute for a proper bottle opener or for fine jewelry.