Brand new hella fuel cap wont fit???

Bought a brand new Hella fuel cap from VW heritage for my 83 tin top GTI
Tried it tonight but it too tight :cry:
I measured the  round part  of the cap that goes in it measures 34.4mm and the original cap measured 34mm.
I dont want to force it on as i will never get it off again.

Its a pressurised cap……the one that they advised for the car.
The fuel filler neck was replaced years ago and its in perfect nick.

Could somebody check the dimensions of their cap for me please.

Any ideas on what to if it is the right cap?

Cheers
Skid.

there are two different types of fuel cap for the MK1 as I also bought the wrong one

I bought this one after research said to get a pressurised one for the GTI.
Also this is the one that  Heritage recommended.
Apart from Pressurised and non pressured , are there a difference in sizes

Can anyone help regarding this?
Could you measure your Fuel cap so i have comparisons?
Nobody has new ones in stock so i can ask them.

Nobody?

Just measured mine. Not sure of manufacturer but it was bought 12 years ago for a 1.8 DX GTI (non campaign). Its marked 'ohne lüftung' (translates as 'without ventilation') 'Made in Germany' and is about 34mm across. The rounded edge makes it difficult to get an exact fig but I'd say its nearer 33 than 35mm. Its quite a slack fit with a mm or two gap when inserted into the filler. Hope this helps.

Thanks for the reply and info.

I just Ordered another one from GSF this time and they were really helpfull.
They took the time out to measure the new one and said it was 34mm exactly.
I am now awaiting delivery of it to see.