HIGH TEMP BUTT SPLICE WIRE CONNECTORS  are not vinyl or nylon covered. Their temperature rating for continuous use at 482 degrees Centigrade which is equivalent to 900 degrees F. and  intermittent use at 667 degrees C.  or  1200 degrees F. makes them good for use in ovens, motors, light fixtures and other applications where other connectors would corrode or melt.  There is no applicable UL or CSA  standard for high temperature steel parts.