This insulator like the larger U-339a has been rather mysterious until recently . Only a handful have been found ... all but one coming from the Victor dump . The recently discovered Locke 1903 catalog had both this, the #30, and it's larger cousin, the U-339a #31 listed. Apparently these two designs had no popularity in the industry and may have never seen any actual use . 1903 seems to have been the only year Locke cataloged ether of these designs .[id=265062845] for more information and to see a photograph of one . the U-339b must have at least seen a decent production run as they have been found with two difrent marking stamps and a variety of glaze colors indicating a quantity was scatted in various places in the kiln The 1903 Locke catalog that was first found and reported by Colin Jung . This priceless historic catalog is now digitized and is a part of Elton's research reference archive. Several other early historic catalogs are available in print reproductions and others in digital form from Elton (Catalog image courtesy of Elton Gish )