Left is the two date version, on the right is the one date version. Also check out Jack Kesling's great comparison pics of variations of Am Ins Co and Postal 156's - [id=79608790] [id=79721841] [id=79721598]. Also, here is one from the Toften collection with the narrowest groove I've ever seen... [id=140736192] Regarding this particular one (from the Toften collection) I wonder if it is a slumper - that wire groove is too narrow to be realistically usable for holding a tie wire. Anyone have any 156s with a similar extreme narrow groove??? Please post a pic to the gallery if you do.