Excellent!  Thanks!

Thanks but how do I know what I'm looking at?  That is, what is the shank?  Is it the piece of steel that meets the block-like thing?  So if it's on top, that's called a "over shank" or what?  Is there a diagram somewhere that explicitly defines this?  I assume that all the couplers have to be the same type in order to mate properly.

I have a Bachmann On30 set, and I need to replace several couplers.  How do I know which to order, i.e. center, over, under-shank; short, medium, long shaft?  Thanks