One of the great challenges in porcelain insulators, particularly very old ones, is that so many are unmarked and very crude in shape. Slight variations in U#'s makes it difficult at times to nail down a specific U# to a given piece. The second challenge is determining the manufacturer. Imperial and New Lexington pieces can sometimes mimic one and other as well as some Thomas pieces. Here are two similar pieces that are most likely different U#'s which could ultimately determine who made them. The one on the right has an overall crude and sloppy appearance. Differing shapes from manual trimming of the tie wire grove can drastically change the profile from machine drawings or catalog renditions. It's part of the mistique that makes them fun!