I don't know but my filler tube is loose. You can wiggle it around and pull it up a tad but not out. I am guessing it just snaps in. I tried turning it clockwise and counter clockwise but it did not turn so that is why my guess is it snaps in.I have 3 dental mirrors and none them fit through the hole in the filler tube. Does anyone know how to remove the plastic filler tube from the valve cover? The service manual was of no help.