There are two sizes, one for 1/8" cable and one for 3/16" cable, the smaller one will work just fine by using our scale adjustment to adapt the smaller unit to read the correct tension as long as the tension on the 3/16"cable is less than 240 lbs.. Almost all of our work has been with the smaller unit. These are important to let you know where you are with the tension. Once a few cables are correct you can almost tension them by tone. You have to work from the center our and then repeat the procedure because the more cables are tightened, the more the ones just adjusted loosen so you need some basis to work from, hence the tool being offered for your use especially if you intend to install more systems.