The studs should have 2 sides: one that tapers on the end and is a little longer, then a small unthreaded gap, then a shorter blunt threaded side. You screw the shorter side into the block until you get to the unthreaded part. Then you just screw the nuts onto them when you install the headers. IIRC, you basically just screw them in until it starts to get difficult and then stop. You don't want to try and tighten them too much cause you could damage the threading in the block. The old ones shouldn't have been in there too tight either.