Also the engine block is made of aluminum. So if you use the wrong thread pitch you risk stripping the threads in the block. $20 is not that much and eliminates any headaches of gathering all the needed parts and fabricating the metal peice that holds the oil plug in place. No its not hard to do if you're mechanically inclined and have the resorces. And to answer your question "will they already know maybe?" I'm gonna say NO....
-My psychiatrist said I needed more Focus in my life, so I bought one.