This isn't a cone wrench but one specifically made for centering side pull brakes back when single pivots were the norm. I believe the "OBW" stands for "Offset Brake Wrench" Now that double pivot side pulls are nearly universal, there is no need for it.

What size open end is at the other end of yours? I have an OBW-1 that has 10 mm and 13 mm open ends.

There was another centering tool I've seen. It was a U-shaped wire with a hook at each end. The hooks were used to stradle the brake spring at each side of the caliper and hold it centered while the pivot bolt's nut was tightened.