Why do these things always land in my lap? I need a tap for some work I'm doing on a Rolls Royce V-12 intake manifold. It has studs in several places, all of them are 13/64" (.203) major dia.x28 tpi. I can't find any reference to a thread this size in Machinery's Handbook or any catalogs. Since the parts are obviously British, any guidance from across the pond would be greatly appreciated. Thanks in advance. BTW will be away from the computer for a couple of hours, please pardon if response is a bit slow.