This is a replacement two fan assembly and comes with 2 - 120mm fans joined by a power wire. The fans are easily replaced by pulling the old fans from the rubber mounts and swapping them with the new fans.
Replacement - When pulling fans from their mounts, ensure to pull gently and work from one corner at a time. The fan mounts can break if pulled too aggressively. When reinstalling the fans, ensure it is positioned to blow air in the desired direction and there is an arrow on the side of the fans which indicates the direction of the airflow.
Polarity. These fans are polarity protected so if polarity is reversed, the fan simply will not operate. Just reverse polarity ensuring that Tip aligns with + on the ends of the connectors