This Fan-Thom II kit comes with a threaded thermostatic switch that screws into the engine block or intake manifold for a professional looking installation. This is inexpensive protection for an electric fan and a vehicle's wire harness. Provides constant voltage, protects from voltage and amperage spikes and prevents the fan from back feeding voltage through the vehicle's wire harness. This kit includes: SPST 40-amp relay, 30-amp circuit breaker, thermostatic switch (195 degrees on/185 degrees off) with thread size: 3/8"-18 NPT, 1/2" NPT to 3/8" NPT adapter, relay base with harness (6' input, 4' output), crimp-on terminals and mounting hardware.