People often ask how to get an accurate ring size. This all depends. For normal, narrow/dainty rings you would use the narrow ring sizers. For regular fit, flat on the inside, wide rings and bands, you would use the wide ring sizers. For comfort fit bands, whether narrow or wide, we recommend using the narrow sizers because comfort fit bands are rounded on the inside.
Most alternative metal bands today are comfort fit, so they are rounded on the inside. It’s best to have your ring sized with comfort fit sizers but most jewelers don’t have these. If they do not, then the narrow sizers work well.
The reason for the different ring sizers is because bands that are non comfort fit, or that are flat on the inside, tend to fit more snug than comfort fit bands as there is more surface area touching your finger.