The 3M black polyolefin heat shrink thin-wall tubing is sold 3 spools per case and is another quality product from 3M. Has a dielectric strength of 900 v/mil. This product starts out with an inner diameter of 0.5 in and after heat is applied it reduces in size to 0.25 in. Along with other changes the wall thickness also changes when this product is used. After use the wall thickness is 0.025 in. The overall length measures 200 ft.