. All heat shrink tubing will shrink lengthwise as well as its diameter; 2:1 shrink tubing will shrink one half of its nominal diameter and less than 7% of its length.Heat Shrink Tubing 2:1- 3/8" x 100FT- Black Diameter: 3/8" Length: 100ft Color: Black This product is UL recognized at 600V and under file No is E180908 or E345553.