The Lionel CTC Lockon replaced the UTC Lockon beginning in 1947 and was issued with every O and O27 Gauge set during the Post War Period. It was used to connect any transformer to the track on every layout except those that were of permanent construction. It snapped onto the edge of the track and provided electrical current to the outside rail and the center power rail. Connection to the other outside rail was achieved though the track ties.
Minor changes occurred to this lockon but none effect the value. It is found either in usable condition, or rusted and/or broken condition.
Lionel dealers sold these separately out of dealer boxes like the one pictured to the right. These boxes are much harder to find than the ubiquitous contents.