Cetre caps for Avus alloys (snowflakes)

Hi
Just bought an awesome set of snowflakes and now need centre caps. Put a vernier across one of the centre holes and it measured 51.0mm which is strange as I have seen that they are 57.1. The problem that I have got is that most sellers quote the outside diameter. Has anyone got any ideas as to what size I need?
Cheers
Niels

Moved to running gear from Engine section.

chortle

Hello, first time I've posted on here.

I'm pretty sure these are what your after. I have them for my Scirocco's Snowflakes and your measurement complies with what I have..
http://www.ebay.co.uk/itm/GOLF-MK1-GTI-CABRIO-9-SPOKE-CENTRE-CAPS-4-GENUINE-NEW-/250996530123?pt=UK_Cars_Parts_Vehicles_Wheels_tyre_Trims_Trims_ET&hash=item3a708f1bcb

You might well pick them up 2nd hand.

they're available from the dealer. (well… they were last summer!)