Hi Morgan......thats what makes it a pain,..the thread really has to be recut on a lathe. You have also really to use a carbide insert tool, and as you are travelling along the original thread, and then hitting weld, it all has to be done very carefully, and there is a risk of damaging, or enlarging, the original thread, which makes the trigger block fit looser. I have only ever done one of these like this, and we had a great old boy on the lathe....it worked O.K., but its not a quick job.....if your cracks are short, and very fine, You could drill a 2-2.5mm hole at the ends...and then put in a bit of dark metal filler....the holes will stop the cracks growing, and all you will see is little dark circle, which is hard to notice (the edges of the holes, inside and outside should be deburred carefully so there are no sharp edges)......Ed