What this means
The IEEE assigned the MA-M block 40F3852 to Beijing Zongheng Electro-Mechanical Technology Development Co.. Every network interface they manufacture under this block has a MAC address beginning with these digits, followed by a unique per-device identifier. If a device on your network shows a MAC starting 40:F3:85:2, it is Beijing Zongheng Electro-Mechanical Technology Development Co. hardware.