Del city 9639 heavy-duty cable ties- uv black- 18", 100 pieces provide up to 50% more tensile strength and 15% larger bundle diameters than competitive product. positive-locking teeth- closely and evenly spaced on both sides of the head provide increased strength. raised ridges on the cable ties bent tips are designed to provide a secure grip while requiring minimal effort to close. the patented- one-piece- injection-molded construction eliminates failure due to parts working loose or breaking off. recognized under ul file # e125869 and meet ul94v-2 flammability classification.