help sump plug size

[pauli]

hi, silly question, but i cannot find a spanner to fit the sump plug on my 88 turbo, i`ve tried both 17-18mm
and also 11/16 but no joy, even the guys in 4 different motorist centres have no clue, it is obviously between 17-18mm but i`m lost HELP,
i only wanna change the oil and it`s taken 3 weeks so far, gotta be setting a record here.

thankyou party people of the elite esprit club


pauli