I have for years and years used Kadee HO couplers in OO. OO gaugers have used these pretty much since they were introduced as they automatically couple with each other and they will manually couple easily with Scale-Craft, Lionel, and most other OO dummy couplers.

On S-C freight cars these couplers work great. Kadee number 5 couplers are almost a drop in fit, with a bit of trimming and filing on the box. The top right car is a box car and the bottom right is a tank car, which show the conversion pretty clearly.

On passenger cars it is a different story. Actually, the number 5 couplers will work on these cars on wide radius curves, but not well on tighter radius curves.

Passenger cars are more sensitive to as to the geometry of the couplers and car ends as they are longer. I have mostly run freight trains over the years, but lately I have wanted to run more passenger cars. This past weekend I finally bought some longer shank Kadee couplers to try, the number 26 coupler. In the photo they are on the cast S-C passenger cars and they did the trick, they allow for a bit more swing between the cars. For those of you operating OO and wanting to run these cars on 26” radius curves these couplers are the way to go.

UPDATE: And now I mostly use Kadee whisker couplers on S-C cars and many other OO applications.