Purchased this summer at a garage sale, I am not able to identify this insulator. Note the long top section and the hole in the top of the insulator

Elton Gish has identified this insulator as a U-190-A Dummy Pothead. Used in the 1920-1950's quite extensively. There is a porcelain cap with metal rod projecting down from the inside center that fit in the top of the insulator. Jack Tod wrote about these in Oct. 1972 CJ: The pothead provides a method of terminating and sealing the underground cable from moisture and a means for disconnecting the overhead line from the underground cable. [courtesy Elton Gish]