Ethernet Adapter Windows Driver - how to find for BCM5701
This is for Windows 7, but should work for Windows 10 

A quick search on the Apple Support site, I was able to find instructions on downloading the correct driver.  I have condensed them here for quick reference:




Download the Netxtreme Mobile/Desktop Driver.  It will say that it's not supported, but the .inf file does include the requisite driver entries
Unzip the drivers to a temporary folder on your hard drive (preferably your Desktop so it's easy to find)
Connect the adaptor to the thunderbolt port 
Reboot Windows 


Windows should automatically detect the adaptor now and install it. You may need to point the installer at the location where you unzipped the drivers. 

If that doesn't work, you will need to do this through Device Manager


Go to Start > Control Panel > Hardware &amp; Sound and open Device Manager 
Click the name of your computer at the top of the device tree 
Click Action at the top of the window and choose Add Legacy Hardware 
Click Next 
Select "Install hardware that I manually select..." 
Choose Network Adaptors 
Choose "Have Disk" 
Browse to the location of the drivers you unzipped earlier. 
Click the .inf file 
Select Broadcom NetXtreme Gigabit Ethernet from the list of drivers available 
OK and install 


You may need to reboot again with the adaptor plugged into the Thunderbolt port to finish the job

Note:  Again, these instructions and driver downloads are for Windows 7.  Thought they should work with Windows 10, it is not guaranteed.  

If having both OS X and Windows 10 support is important, consider getting a USB 3.0 to Gigabit Ethernet Adapter.  I have personnaly used this exact adapter on an iMac, a MacBook Pro, a Mac Mini (Dual Boot w/ Win 7) and a Surface Pro 3.