I just went out to the garage and dig out 8 sets of head gaskets. 3 sets of FelPro 8553 2 new, 1 used, all three measured .050, 2 sets of factory gaskets measured .046 and one was .036. 1 set of Mr Gaskets measured .036
On a well used gasket, find a spot where the gasket has been pinched and measure there, not the fire ring ;) then account for that .004-.006 crush on the new ones.