Use instructions:

Please choose the correct cooling fans for different applications. 
        For 4-6 cell NiMH or 2S LiPo: No need to change the 5V cooling fan on the ESC
        For 7-9 cell NiMH or 3S LiPo: Please choose a 12V cooling fan or supply the 5V fan from the receiver (+6V)
        For 10-12 cell NiMH or 4S LiPo: Please choose a 12V cooling fan, and cut the output of the built-in BEC. Then supply the receiver with a UBEC (An additional external DC-DC regulator)

Specification

Size:   5V: 24.5mm (L) * 24.5mm (W) * 10mm (H)
Weight: 7.2g 

 

High-Performance Cooling Fans for HOBBYWING ESCs come in various sizes and power voltages. Each unit is checked and approved via ISO 9001 Quality Control procedure.