Atlas’s "Sidekick" is a nice tool to use for installing certain rail joiners. Compared with either manual joiner installation or just using another piece of rail as a jig, the Sidekick has a distinct advantage, namely, you load it by lightly pressing a rail joiner into a slot at the end of one of the Sidekick's "wings." This is helpful for those of us who have a hard time holding parts steady and/or sliding small parts into place. I can only speak to HO gauge, but be advised, this tool is designed for use ONLY with Atlas Code 83/Code 100 rail joiners. Probably not a good idea to purchase this device with the idea of using rail joiners for smaller codes of track, except for Atlas N gauge size, or for that matter, any other brands of track or rail joiners. Take a few moments to customize this tool by cutting off the “wings” for gauges other than your own. Otherwise, with HO and N at least, parallel track that’s already in place will very often interfere with the Sidekick's operation. The "wings" you remove remain useful for their respective Atlas track gauges.