Speedometer cable

Had the same problem with my Duster. Has a non-original 727 (was originally a 4 speed car). The Duster piece had the small threaded end. I found the cable for the 69 Charger was correct with a 7/8"-18 Female end and worked perfectly. Here's the part number for the one I bought from Advance Auto.

http://shop.advanceautoparts.com/p/atp-speedometer-cable-03192/5013348-P

Hope this helps,
Pat