Looking at the engine I have on my bench, I would say that it is a strate thread. There is a gasket between the fitting and block. If you would like I can send you a photo of the fitting/gasket/block, I am not removing this fitting at this time. If there are any other things you need to see I can e-mail you photos, I have this engine apart for new rings. Now I maby you can help me out. I need a photo or drawing of the oil level float assembly, all I have is the pointer on the out side of the engine. My e-mail is interlakesautorepair@yahoo.com Thanks Peter