Owfeel PC Fan Connector PWM Thermostat 4 Pin Female To 2x 4pin/3pin Male Extension Cable This extension cable enables 4 pin connector on the motherboard PWM speed control and thermostat 2 PWM fans simultaneously. The extension cable is to keep the air flow balance and prevent hot air backflow when the chassis fan has no acceleration. Dual PWM fan, ideal to make the fan quieter and achieve better heat dissipation. Owfeel(TM) is our registered trademark,we will attach 3D copyrighted card,pls don't infringement. Note: In order to make sure correct CPU fan speed ,one of connector has no tachometer line(3 lines only), which is because two 4P plug separated from motherboard can only support one way velocimetry.