i can still see the end of the thread only one thread but once the gasket is on its well below the gasket face. i would only say 1mm of thread really but the end two if they are screwed in the shoulder is below the deck height of the block i have cleaned the threads with a m12 x 1.75 tap, was thinking maybe i need to use a blind hole tap, the bolts bottom out in the block on all studs other than the end 2