Mike
Yes as Walter says, mates right up with Lionel O tubular same rounded top. It is better IMO because unlike Lionel track, the 2 outside rails are isolated and it is easy to make outside insulated rails to activate accessories. My layout has an automated block system using relays so this is a big plus for me. Lionel type uncoupling tracks,accessories etc, join right up as does O-27 with a some conversion pins. My other layout is Atlas NS but I like the K-line just as well and it is much cheaper. Here are a few pics of some O-120 I purchased years ago. It is also a surprising quiet track for tubular,I think due to the thick plastic ties..
Click on the photo to enlarge. On the floor,bottom right of the first photo you will see part of a relay bank which switches the trains to keep them from colliding on a loop.
Dale H
