P/N 51437-6 and 51437-7 were the latest correct hubs for the A,B,C helicopters when modified with the 9-12 degree head. (S.B. 51)The later -9 & -11 hubs were for the D & E but will physically fit the earlier models. I do not know of a -8 hub. You would be OK with the -7 on an A,B,C aircraft.