U50 & U51 / UA51 came with various IHC & Deering planters & seeders -- the hook on U51 and UA51 was either a spring puller or worked somehow with the flexible tubes that the seed flowed through on the way from the seed box to the planting shoe. U50 is called "socket wrench" in the parts lists condensed in Gil Irps' IHC wrench compilation, and U51 / UA51 is called "socket wrench handle."