The amount of shrinkage obtained when working with PTFE shrink tubing depends upon several factors. The biggest one is the diameter of the object where the tubing is being applied. You need to determine the diameter of the object and use this information to help you select the right size of shrink tubing. Shrink tubing wall thicknesses and inner diameters are based upon both preshrunk and shrunken states. The resulting insider diameter and wall thickness depends on whether there are any restrictions. Restrictions prevent the tubing from fully shrinking.
For example, shrink tubing with a 2 to 1 shrink ratio normally has about a half reduction in the starting inner diameter and the recovered diameter. If you were to shrink a piece of tubing with a 0.50 inch starting diameter, with no restrictions, the resulting diameter would be around 0.25 inches. However, if the diameter of the object where the tubing is being applied is greater than 0.25 inches, then the actual resulting diameter will be larger. Further, the recovered wall thickness is less if the tubing is restricted during shrinkage.
Restrictions are just one issue you might face when working with PTFE shrink tubing. Another problem which sometimes occurs is where the tubing is allowed to fully shrink without restrictions, but ends up not fitting firmly around the object. This mistake is the result of using shrink tubing that is too large to fit around the object. It is easily fixed by determining the actual diameter of the object and matching tubing with a recovered inner diameter as close to this measurement as possible.