1981 XS400 SE valve seals

[Firestone]

Hi, are the outlet and inlet different sizes?
11 and 10 millimeters?

I can see here that there are two and two, but they are the same code?
https://www.motomike.eu/en/vehicle/yamaha-xs-400:21046/category/10400000000/?sr=30&show=gal_kombi
Can't find measurements anywhere.

 

[Firestone]

 

[tstidham]

When I did my head, the valve seals were all the same.

 

[Firestone]

I had one too big, not sure if the seat had been replaced or the valve seals were just bad quality resulting one to be a bit wider, but got a different one and seals replaced. So fyi, all 4 seals should be the same.