Autometer Mechanical Speedometer Issues

Hi everyone. I have a 1974 Plymouth Scamp that I am putting new autometer ultralites into. I got a brand new Speedo cable from Napa and an adapter from classic dash. But when I got everything my Speedo cable has a plastic clip on which isn't working with the adapter. So I'm reaching out to see what others solutions are and find a way to fix this. Thanks!