If the stud breaks off, drilling is the easiest way to get out thestubborn piece. When the stud breaks off flush, it means corrosion hasmade the stud and manifold become one. If the broken piece is not flat,use a handheld grinder to flatten out the stud; this allows centerpunching. Carefully drill completely through the broken piece of studwith a 5/16-inch drill bit. If the drill bit is centered carefully, acenter punch can break out the remnants of the stud. Tap the threadswith a 3/8-16 tap. An "Easy-Out" stud or bolt removal tool can be used,but in a situation like this they almost always break off and things getreally messy. Easy-Outs work when there is minimal thread resistance,and in an exhaust system there is no such thing as minimal threadresistance.