Any question answered...

I gave my friend an old road wheel that I used a 9 speed Campagnolo cassette on, he bought an 8 speed Record cassette for it but the lockring doesn't fit the hub.

The lockring has an OD of approx 29mm and the freehub and ID of approx 26mm.

Does anyone know if he can buy a new lockring to fix the problem? If so which one?

Apologies if this is really obvious, gears are still a bit alien to me.

Campagnolo changed the spline pattern on their hubs as part of the move from 8 to 9 speed so even if he has the right lockring the 8 speed cassette will not fit.