What are press-studs?

Answer 1

The press-in studs are on the cylinder heads. That's where the rocker arms go. Press-in studs don't stay in very well in high performance applications, so most people either have there heads machined to accept screw-in studs, or buy heads that came with screw-in studs.

A low-cost alternative to screw-in studs is to have the press-in studs cross drilled to accept roll pins to keep them from pulling out of the pedestals.

This only applies to iron heads, as aluminum heads always come with screw-in studs.