Shown here are the two distinct versions of the Locke U-964 On the left is the later version produced from mid 1903 to about 1905 . on the right is the early version produced in 1902 and early 1903 the early version has a distinctive crown and a full mold line that bisects the entire top skirt from rim to rim. The later version only had a mold line over the crown extending down to about 1/2 " from the tie wire groove . This intersects another mold line that circles the crown. The early ones seem to be a bit scarcer and are often very thin and fragile where as the later ones tend to have thicker skirts and are generally beefier . The unit on the left was recovered from the The Fonda, Johnstown And Gloversville interurban on a section built in mid 1903 . The unit on the right came from a switch house at an old saw mill in central Mane. Both of these insulators were widely used on early electric railways in the east and midwest. Here is a top view of both crowns [id=369502967]