Speedometer Cable

I bought a replacement cable last week from Kragen and the one that they gave me is the same on the instrument cluster end but does not match the transmission end. My original cable has a large nut on the end that threads into the transmission. The replacement has a smaller round "hand thread" type nut. Took it back with my old one to compare and they were no help as they said that was the only part number for my car. Looking at most of the pictures online at other auto parts stores they look like the one Kragen gave me. By the way my car is a 70 dart swinger 318 with a 904.