This is another version of the metal cased composition trolley insulator. This one has moveable clamp 'arms' on top. This one is marked on the front skirt: 211 (it's upside down) and reverse skirt: PAT MCH 16 1897. I believe this refers to patent #578,825 assigned to Luscomb for the Johns-Pratt Co. Info from page 167 of Tod's A History of the Electrical Porcelain Industry in the United States. This insulator stands 4 3/4" tall. See also the metal trolley cable insulator posted by Bill Meier here: [id=249674362]