Yep, the old stripped torx on the infamous thermostat housing. I don't know for sure but I suspect the reason for there dang things is that the average Harry Homeowner doesn't have a set sooooooo, it's off to the dealer for routine repairs. Most of this stuff is desigined to eliminate the shadetree mechanic and force him to take the car to the dealer for big $$$ on simple repairs. That's why forms like the BB are so valuable. It's saved me thousands over the years. Hex head cap screws are much more convenient IMHO and less likely to strip out the head.. On the torx on the thermostat housing, a universal joint extension or a wobble extension helps a lot. My guess is that a metric cap screw of that size (probably a #10 or 11) would work