Well, you would purchase one for every two kessil mounting kits you have. This is an extension rod for the mount kit so it can extend down to the cabinet. The mounting kit only comes one each the extension rod is 2 each. The mounting kit comes with everything to mount both, the extension rod is just that a rod and connector. I would check everything out before you get too far into it. Does come out to be pricey going the way I did. That is why I haven't done it yet cause I already dropped 130 just for the kits and another 55 just to mount to the cabinet. Sometime I can't justify doing it. Yet, every time I think of adding a screen to the tank it would be so much easier not having the lights mounted on the tank.