Just shy of snug start in the middle, then work your way out criss crossing.
Once sorta snug, then tighten a little more on the 1st pass in the same sequence: middle - to the outside.
Then one last time, tighten a little more in the same sequence. Does not need to be "TIGHT" just very snug. The header against the gasket seal will work. Too many people want to over tighten and then problems occur.
Answers & Comments
Just shy of snug start in the middle, then work your way out criss crossing.
Once sorta snug, then tighten a little more on the 1st pass in the same sequence: middle - to the outside.
Then one last time, tighten a little more in the same sequence. Does not need to be "TIGHT" just very snug. The header against the gasket seal will work. Too many people want to over tighten and then problems occur.