Thanks, I figured it had to be fairly large, judging by the number of fins. I have some fresnels that are 5.25 by 5.25 but haven't figured-out what lamp they fit. I don't have any 1880's Dietz catalogs, but looked this up in the 1883 S.G.&L. catalog since Dietz and SGL used the same patents and made the same lanterns. This lamp is nearly identical to the SGL Tubular Marine and Bridge Signal Lamp they show in 1883, so it's certainly an early 1880's product. The catalog shows a No.1 (5/8" wick) and 6" globe or 6" fresnel, No.2 (1" wick) with 8" globe or 8" fresnel, and No.3 (1.5" wick) and 8" fresnel.