what fastener is used for #516 valve cover

metric? I can not tell by looking at it. this is a std 1967 #516 head, I have the 5/16" cap screws that is used in the sixth hole. the other 5 are what looks like 5/16" studs with approx 22 threads per inch. I have many different kinds of fasteners in my shop nothing comes close to this, did they use metric in 1967? what I could do is to use my vernier calipers on the stud and they go to home depot and look at the metrics and buy something that looks like it has the same threads per inch with the diameter I will get from my calipers.