Ok, so I checked my stock and I have T-20 , #8s in GRK boxes.
HOWEVER - they aren't GRK screws

. The original ones are T-15s - I must have put in spax brand ones at some point.
This brings up an interesting point raised by a few here. What's standard or common?
Seth says, T-15 ; I say T-20 ; and I had a look at a supplier today , and their two brands of #8s both had T-25 heads .

. So it would seem there is no standard.
I prefer T-20 as it is more common for more of the fasteners I normally want to use for cabinetry and on the German appliances we typically specify. I can see where T20 might be a bit wimpy for framers or deck guys working hard all day. I just can't remember the last time I ran across something with a T15, which is prob. why I re appropriated the GRK boxes to hold screws with T20 heads.
I guess "common" all boils down to what's available at your local supplier.