These are basicly the same insulator except for the fact that the U-955 has been designed to fit a 1 3/8 pin ... likely the U-955 was a custom special order ... Only three have been found thus far ... All werefound on the west coast in northern California or sothern Oregon antique shops or shows. The historical use of the U-955 remains unknown. The U-675 is compairitively much more plentiful in collectors hands [id=342989995] for a compairitive underside view of these two insulators .