Perhaps the most common 6 inch porcelain suspension around. The OB in a dark brown and some of it's many cap markings. Some also have the porcelain bell etched, 6 OB 1, 6 OB 4, 6 OB 5.

*Note cap marked 1961 and bell etched 6OB 1 are not on the same suspension.

I recently sorted through several hundred suspensions keeping just a few for display. Who'd thunk it that a suspension, particulary a brown one, had any interesting features.