The 200-FAN fan base is an option for the 203 and 205 LaserMounts for applications that require greater thermal performance. By using a small fan to force air across the mount's heat sink, the efficiently and performance of the mount is significantly increased. For the 203, this means a thermal performance increase from 2.3°C/W to 1.0°C/W, while the 205 has an increase of thermal capacity from 3W to 8W. Installing the fan base is easy... simply remove the 4 screws from the bottom of the mount, replace the standard base plate, and screw on the new fan base.