Add-A-Snap - Black - 2-1/2 For use with canvas or nylon boat covers, the Add-A-Snap allows you to easily add length on hard to reach snaps from shrunken material. Nickel plated brass/nylon.WARNING: This product can expose you to chemicals which are known to the State of California to cause cancer, birth defects or other reproductive harm. For more information go to P65Warnings.ca.gov.