External Cap: - Made of rugged, thermoplastic polymer material and 150 degrees C-rated. - Insulator cap locks securely in place to safeguard against accidental loosening in high vibration applications. Inner Sleeve & Screw: - Choice of Slotted or Robertson screw-driver installation. When tightened into the insert, provides a solid pressure type connection on all approved wire combinations. - No need to “re-strip” wires when rewiring. Simply loosen set screw to remove non-twisted wires. - Brass sleeve + set-screw help resist corrosion. Approved for circuits up to 600V, and lighting fixtures and signs up to 1000V. - For copper wire only. - Convenient packaging - sized right and job-site ready!