Abstract: A method of rebuilding an annular blow out preventer of the type having a head with threads that attach it to the body of the blow out preventer involves the removal of about 1 to 11/2) of the threads (e.g., if total thread revolutions equal seven (7) revolutions) closest to the internal bore and piston of the apparatus. An annular groove is formed at the interface between the head and the body. An annular seal, preferably a lip type seal, is positioned at this interface at the annular groove. The seal isolates the threads from the upper hydraulic chamber that is used to move the piston portion of the apparatus. This method prevents contamination and/or corrosion of the threads.