Hi All, A friend owns an A4 B6 Avant and has damaged the nut that holds on the rear wiper arm. He says he used a 13mm socket to get it off. Can anyone tell me what size nut he can replace it with? Is it an M13? I've tried searching and can find reference to the 13mm nut, but not specific mention of the type of nut so he can order a replacement. Thanks.