Off hand, I don't know of any washers that go around the probe. If memory serves me the probe fits into a fitting that is screwed into the exhaust manifold. If the fitting is 1/8" npt, Then you will need an 1/8" pipe thread tap. If the fitting is adapted to 1/4" npt (like my di pricoles) then you will need a 1/4" pipe tap. If you go to the hardware stor to purchase this tap it willtell you right on the package what size drill bit to use. I would tell you, but I don't have my Machinist Reference book on me. Also, if you don't have a few chuncks of magnet laying around the house, grab some. Sears for about a buck gets you 2 in the tool area. This will help to keep the majority of the chips out of your turbo. If some fal in I wouldn't stress. Your exhaust will blow them out long before your turbo gets a movin. Good luck, and glad to see you aren't afraid to do the wrenching on your truck!