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I have 20mm on back, have been thinking about front ones. Have sent @Zedcarz a pmYes, they are. 12mm on the front and 20mm on the rear. The same spacers were removed when I sold my Z3 and fitted to my E85 Z4 (they’re still on it). I also fitted the same sizes on my E89 Z4. Pitch and centre bore are the same.
Tony.