cob was avalaible through the early to mid 60's. during the transition time in 64-65, you'll even see drums with one brass and one steel. after that, they were primarily chrome over steel hoops.

mike

Ahh, cool. I've a keystone badged Supra but I don't think the batter rim is COB, thanks for your help sir :)

It wasn't an optional thing. They had made them out of brass for years and then switched to steel in the mid sixties. Ludwig didn't mention or advertise what material was being used although at the time no one was paying any attention to what hoops were made of anyway. Like Mike mentioned they would just grab the hoops they needed off the pile and put them on a drum they were building so for a while the occasional drum might end up with one of each until the supply of brass hoops was finally used up.

If a magnet sticks it's steel...no magnetic attraction then it's brass.