I'm resurrecting this old thread to finally provide the answer after lots of trial and error on my end. I hope this makes it easier for someone in the future and saves time and money.
The correct size is a 1/16" hex - I'd recommend the Wiha Precision Screwdriver, as it allows you to more easily turn it than the standard key.
The correct size is a 1/16" hex - I'd recommend the Wiha Precision Screwdriver, as it allows you to more easily turn it than the standard key.