3M(TM) Highland(TM) Wire Connectors make it quick and easy to match the right connector to the size of the wire. The shells are designed to withstand temperatures up to 221(deg)F (105(deg)C). 3M(TM) Highland(TM) Color-Coded Wire Connectors are UL Listed, CSA Certified, and work equally well with either solid or stranded wire. H-31, H-33 and H-35 connectors are rated to 600V (1000V in signs and lighting fixtures).