that you can buy. Fit an extended 3/8 inch socket drive into it and undo by turning counter clockwise. Mine is a Vector, part number 17001 and is marked 76/14 which I think means 76 mm and 14 sides. I don't remember where I got it - probably at an auto parts store. It is not necessary to really torque the cap down after changing the filter. I do hand-tight plus 1/4 turn and don't have a leak. Also, loosen this all the way before you drain/extract the old oil so that the filter will give up the oil it holds.