Ideal Wire-Nut wire connector features fixed square-wire spring to provide secure wire connection in bare copper wire. UL 94V-2 flame retardant shell is rated at 221 degrees Fahrenheit and 600 volts. Reusable for easy repair and changes. UL (Underwriter's Laboratories) listed to 486C and CSA (Canadian Standards Association) certified to C22.2 #188. Compliant with Federal Specification w-s-610E.