When purchasing a PC case fan, you can choose between a 3-pin or 4-pin connector. Only use them if your motherboard lacks fan headers, and you can't afford to or find a fan hub to connect current three or 4-pin fans. There are also fans with a 2-pin connector. The majority of these are found in the power supply. These should not be purchased for your case. Choose between 3-pin and 4-pin PC case fans unless you have an exceedingly ancient, very particular, or exotic PC with proprietary connectors.