I used a Philips #1, but had to search the workshop for one that would fit well, and found one in a "cheap" Bosch bit-box. My trusty PB roll also had the right screwdriver. They are very tight or Asrock used Loctite, but that would beat the purpose of the barebones that MUST be opened by the end-user.

I had to try a bunch of different screwdrivers, the one that finally worked was bigger than I expected. I don't have the exact specs, though, sorry