….how do they get their wheels back at the end of the day? Presumably they put a mobile number or a name on the wheel and go along and find the mechanics to swop back?

Good way to get some nicer wheels 😉

Do you mean the guys standing at the side of the cobbled sections holding up wheels? They are team helpers.

If a rider gets a wheel from the Mavic neutral service then the team mechanic will have to take it back after the stage and get the team one back for repair.

Find it amazing that the wheels the neutral mavic bike and cars offer actually fit all the bikes. Do roadies have standard cassettes, axle sizes etc?

All the 11 speed road cassettes have the same spacing now. They’re all QR and 130mm OLN.
Just wait for about another 18 months and here’ll be about 19 different standards for dropouts and fixings and neutral support will be gone.

There will be a 730c wheel size to make the road come alive.