The most common suspension I come across is the brown OB with a date on the porcelain. The greenish one is the first other colour I have picked. I remember the dumpster had many strings in all colours with HYDRO marked on the cap - all the rest were damaged, but I will assume all were similarly marked 3(OB)9 . Also in the same dumpster were a number of CP discs with a 1939 date. Many were damaged but as they were on top, many were good enough to save.