Our Black 4 inch Nylon Zip Ties are tamper-evident to help secure bags, electrical wire, cables, or plastic piping permanently. The self-locking seal creates a durable, no-release, no-slip fit. 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 18 pounds and come 1,000 to a case.