That is a 6x4 zinger. I had it laying around. Usually I'll run anything from a 5x3 to a 6x4 on my cox's. The hotter the motor I found the smaller the prop. On a bone stock baby bee I think they like the old 6x3 or 6x4 topflights. I'll start with a 6x3 on the BW and go down from there.