These funny mushroom shaped porcelain pintype(1-3/8" pin) insulators that do not have any groves or saddles for a wire is actually an arcing horn arrester. This style was made by Ohio Brass in the mid to late 1920's. they were used on the ends of arcing horns at the end of a string of suspension insulators. The purpose was to control the flux or arc caused by electrical surges such as lightning.

Height: 7" in. Width: 7.5" in. Weight: 6-7lbs