I am replacing the blend door actuators on a 2000 corvette and I cannot find a socket that fits the screw heads.
a 6mm is to big and a 5mm is to small. 1/4" is the smallest standard size socket I have and it is also to big. Any one have a guess on what size I need?

5.5 I think

5.5mm or 7/32"

Yep, 5.5mm hard to believe isn;t it! 7/32 will work too as above poster said. For some reason 5.5 is a very popular size.