It is "exactly" - 56mm across the face of the insert. I had to bend the ruler quite badly to measure it because the insert is so sunken into the wheel. Mine won't prise out I think -I had to pop em in from the back before they went to ATS to be fitted to the car. As for the availability, I had to order the four inserts, but it only took about two days to get to the dealer, so I was quite chuffed with the promptness.

Exactly 58mm using a bent ruler?

Reminds me of a film some years ago in which one of the (female) characters used scissors to make jigsaw pieces fit. (Lest I be branded sexist, had the part been for a male, a hammer would probably have been used instead).

well, the ruler was straight across the insert, just bent into the wheel... I seem to remember Homer doing a jigsaw and just thumping the pieces together when they didn't fit. I haven't done a jigsaw for ages, but I imagine my tactics would be quite similar

Bummer! The Radius inserts are 62mm across the face and 54.5 on the spigot that goes into the alloy. Time to think again .....

Thanks for your efforts Jason.

I forgot to measure the spigots, but I suppose being 4mm out on the face is bad enough. If you want I can post one of my VW inserts to see if they fit, then you'll know the Skoda one's will too. (or if poss, take a wheel into your dealer to do a "fit before you buy")