These Ohio Brass ( OB ) M -2751A metal clamp tops were all sandblast OB date marked 1955. An under rated OB when you include the complete hardware set up. The California Oregon Power Company ( COPCO ) used these and the bigger brother M-3637 with metal crown inserts on many of their transmission lines throughout Southern Oregon and Northern California service areas. These were rescued from service after many years on the job! Additional views to follow.