What is the specification of the extra screws needed to install a second drive to an upper-drive populated Mac Mini 2012?
According to iFixit's HD replacement guide for Mac Mini 2012, you need both a T6 Torx screwdriver and a T8 Torx screwdriver. The guide shows the corresponding screw specifications for each relevant step (IE two 6.6 mm T8 Torx screws), but iFixit only sells the screwdrivers, not the screws themselves AFAIK. They do, however, supply you with the information needed regarding all the relevant screws.