Layshaft 'o' ring size and material?

[AlG]

What size is the layshaft 'o' ring?
I have measured 22mm internal diameter by 2mm cross section from the current one, but the cutout in the layshaft is more like 2.5mm.
Also, is Nitrile rubber OK, or should I go for Viton?

Cheers
AlG

[AlG]

So all the dealers appear to sell 20 x 2 mm in Nitrile so I will pick up one of those and compare it to the current seal. If the fit appears the same then I will go with this.

[Warkton Tornado No.1]

The 'O' ring size is 20 mm x 2 mm.

IMHO, Nitrile remains the appropriate material choice for seals & 'O' rings for all applications within the Lambretta, though in the case of the carburettor float needle, my own reasoning is that as replacement is so rare & the cost difference only marginal, Viton would be the better choice.

I hope that helps.....