Speedometer cable issue

I bought a new speedometer cable for my '70 Duster and it seems like I'm missing something between where it hooks up to the drive pinion on the trans. Anybody have a picture of how it goes? The threaded part of the pinion drive is much bigger than the threaded nut on the end of the speedo cable; is there a separate adapter that threads onto the pinion and has a smaller end to screw the cable onto?