Haven't found another hook like this in any of the insulator reference material, but can't say as Ive seen everything ever documented on hooks either. This is 5" x 1 1/8". The black part is gutta percha or ebonite. The large threading is uncommon. The collar around the hook is unusual also as they are usualy flared. No eveidence of any markings. Came from the east coast region. It could possibly be an insert part from another style of suspension insulator ( like the Siemens No1). Would be interested to hear of any similar ones in captivity. Thanks.