Our Black 6 inch Nylon Zip Ties are Tamper Evident to help secure bags, electrical wire, cables, or plastic piping permanently. Self-locking seal forms a durable, no-release, no-slip. UL approved. Ties are easy to use: just insert the tapered tip into the lock, tighten to tension, and trim off excess. Black Zip Ties stay locked permanently and will not stretch. Heavy Duty Nylon Zip Ties are the strongest solutions for all heavy wire & difficult cable management needs, HVAC duct installation and repair, automotive detailing or car organization as well as law enforcement, and any sort of around the house project. They have a tensile strength of 40 pounds and come 1,000 to a case.