Yes I read the ad and it says for front and rear hubs for the Calibra but also says its a driveshaft hub nut (4x4?).
I have read somewhere that the fronts are 30mm and the rears 32mm and the Calibra is my daily driver, an 8 valve 2wd.
Then again I could be talking complete tosh, as hardly anyone changes the rear bearings so there's not much info out there.