The Ray-Ban RB4291 is a single-size frame, 58mm, with a square plastic front and 145mm arms, sold as a unisex model. Its aftermarket tint list matches the wider Ray-Ban range — three gradient shades, eight mirror finishes, a photochromic grey, and a clear AR lens for prescription wear — so there's no size guesswork, only a color decision.

Since there's only one size to worry about here, the real decision on the RB4291 is between a fixed tint and the photochromic grey — useful if you wear the frame both driving at dusk and outdoors at midday, since that lens adjusts instead of forcing one fixed darkness. A plain grey or brown solid is the safer pick if you mainly want to match the tint you already have, rather than change the look of the frame.