Teflon heat shrink tubing is available with different size diameters. The size given refers to the preshrunk diameter size of tubing. You have to know this diameter in order to select the size tubing you require. You should select sizes based upon the diameter of cable or wires where you want apply tube. In addition to using the preshrunk diameter, you will also need to take the heat shrink ratio into consideration.
Understand the Ratios Used with Teflon Heat Shrink Tubing
You will need to understand heat shrink ratios when working with Teflon heat shrink tubing. These ratios tell you how much the tubing shrinks from its original size to its shrunken state. For example, if you had a section of tubing with a ½ inch opening and a 4:1 ratio, the tubing would shrink down to about a 1/8 inch opening after fully shrunk. On the other hand, if you had the same size tubing, but with a 2:1 ration, the tubing would shrink down to about a 1/4 inch opening.