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 185°F On/175°F Off (thread size: ⅜"-18NPT), ½"NPT to ⅜"NPT adapter, relay base with harness (6' input, 4' output), crimp-on terminals and mounting hardware.