HO scale 1/87 Miller coupler. 2 pairs. Fits in a ordinary Kadee pocket (for example a no 5 coupler).
Vital that the coupling travels smoothly from side to side otherwise the coupler can uncouple on curves.
Tested and works well on 20" curves and over. Off course depending on the length of the cars. Also critical that the couplers is fitted to the same height on the cars. Uncoupling done using a toothpick or similar pointy object.