I got a part number of STN112X for the course thread, and STN102X for the fine thread. However it lists the size as "3/8 in." which must refer to the inside diameter. I couldn't go to the NAPA store after I found out this vital bit of news because it was closed. Apparently you don't ask for them by the wrench size, which is 9/16". Thanks for the advice. Now I just need the intake to exhaust manifold gasket... the correct one was not included in the manifold to engine gasket set. I've allotted all day to trying to use the internet to track this stuff down. Guess I should just ask a knowledgeable KF member and get it done right.