Kadees And Minimum Curves

All depends on what Kadee coupler you use (short shank, medium shank, long shank) and if you have diaphragms and how close you want them spaced/touching.  Most applications on 0-72 you should be fine.

I can tell you that I have 18" cars and I needed the long shaft coupler for them not to derail on O-72 Scaletrax.   I'm guessing 21" would definitely need the long shaft.

Have Fun!
Ron

@Ron045 posted:

I can tell you that I have 18" cars and I needed the long shaft coupler for them not to derail on O-72 Scaletrax.   I'm guessing 21" would definitely need the long shaft.

Have Fun!
Ron

Which coupler is that (i.e, #740, #747,etc)?

The long shank couplers are #746 - metal couplers with plastic gearboxes - two pair to a package.

@Richie C. posted:

The long shank couplers are #746 - metal couplers with plastic gearboxes - two pair to a package.

Are there any with metal gearboxes

@Justin Acuna posted:

Are there any with metal gearboxes

You can buy metal gearboxes if you really want them.  #818.  I would try the stock ones first.  If you don't like them, then go for the metal boxes.

Ron

In addition, Kadee (and common sense) recommend that you do not use metal gearboxes on metal frames in order to avoid potential electrical issues.