Ah .... I see. I have just phoned him and it seems he has just learnt something new about his bike (had it since new in 1997!). He is very grateful for the info though, as he now doesn't need to buy/carry another socket. He figured taking odd sized ones would be wise in case he got stuck out in rural France. He has the C spanner so he'll be fine.
Thanks for the swift reply Jon.
Threaded Mode