this depends on what fitting your using... there are earls fittings that are -10 an that use NPT adapter on the other side, and there are some that use NPSM on the other end, so your best bet if to find out what size threads are on the other end of the fitting, and what kind of fitting it is.
also if this is for your valve covers, they make weldable -10 an fittings that can be welded on also.