Allen Head Size for Rear Rack Install?

[widude]

Hey, My new rack comes today. I just did some checking, the 6mm is to small, the 7mm to big. Are those rear allen heads 6.5mm or so? The ones that need to come off to install the rack.

I may have to do a tool run anyway later, just thought I would ask here before I ride to the tool shop and see what fits.

Since they may be tight, I may need a head that will attach to my socket wrench? Thanks.