These" plug in "units are well constructed and very simple to fit. The bases if retained can later be used for separate bulb replacement although a little skill and appropriate fine tools and perhaps a magnifying glass would be useful for this work. Like some Scalextric spares they are often hard to find . There are, of course, other ways of lighting Slot Cars set up for this system of lighting but these ways are more taxing to follow and often require acquired skills including the use of a small, low power soldering iron . The "plug in" units are the obvious choice if speed and simplicity in repair is a priority.