11mm x 1.25, ARP has the proper bottoming tap.
To properly install head studs you must tap all the threads to remove debris and shit. Then apply a thin layer of ARP moly lube to completely coat the threads of the stud. Install stud and remove stud about 5 times. This will ensure that the lube is distributed among the threads properly and that the friction of the threads is minimised. Tighten them hand tight. I like to add a tiny snug with the appropriate allen key. Then do the same with the threads that are going to be securing the head down. Use the nut to run up and down and spread the lube. This way again you zero out the friction.