Nut looks to be like 19mm but my 19mm socket is a bit loose. Nut is very tight has not been removed in over 10 years but I desperately need to get my spare tire out and mounted. I tried WD40 but its real diffuicult to apply it and so far it refuses to yield and the socket continually slips. Anyone got any ideas? Personally, I think the whole concept of needing a special tool to access the spare tire is a dumb design.