Which Fuel tank?

[buggycal]

This is going to sound daft but, i am looking to change the fuel tank in my 81 T25 Aircooled van, however i am told that there are two sizes 48mm and 68mm and i believe that is the fuel filler size, my simple question is this, where is this measurement taken, the filler neck, hole in tank where it enters. i have measured both and neither are 48 or 68mm. any help would be appreciated.

[dink]

follow down the filler pipe to the bottom there it does through the chassis,measure the diameter there, I think the 48mm or 68mm refers to the hole in the tank
so if you filler pipe is smaller than 68mm but bigger than 48mm then I'd assume it's 68mm, similary if it's smaller than 48mm then I'd expect it to be 48mm

I'm pretty sure you have a 68mm fuel neck

i think it was the later T3's that had the smaller 48mm filler neck

[Andy syncro-nutz]

Think if you have a steel filler neck its 68mm And if its plastic 48mm???