Size 12. Lightweight aluminum. Classic 1940s signet ring style - midcentury modernist / machinist. Very well made by a serviceman who had access to industrial tools like a lathe or drill press, polishing machines - I think I can see the threads on the inside so it may have originally been a piece of piping. Rectangular head is nearly 1" wide x 5/8" and engraved with a deep diagonal line. Dynamic!