Oil plugs....if the threads are good in the oil pan I like the one with the built in rubber O ring. Over the years I have slipped a rubber O ring over the plug and never had any problems. I guess, like tcox said, that the rubber as well as the plastic conform to the surfaces better?.

1937 Chevy Pickup
In the Gallery
1952 Chevy Panel
In the Gallery
More photos
1950 Chevy Coupe
Pictures!

I'd rather walk and carry a Chevy hub cap than ride in a Ferd.
I can explain it to you, but I can't understand it for you smile