heres the most common sizes I encounter: 10mm 12mm, 13 mm, 15mm, 17mm. like stated earlier you can just about fix anything with 10mm and every oil plug i have seen was 17mm. the only big azz size i need was like 32mm for my axle nut on my 96 odyssey. Everything should be metric on all hondas. if its not, then someone else put it there after the fact.