If it's like the spark plugs for any other Audi or VW I've ever worked on,
then it's a standard (i.e. not the smaller type found on many French cars)
plug socket. Most socket sets have a special one for the spark plugs. This
is marked "14mm" but it isn't 14mm across the flats. Actual size is
approximately 20mm, but you'd be best advised to get the proper tool - which
has a rubber insert in the deep socket which holds the plug and prevents it
falling out. In may experience whenever the plug falls out of the socket
it's on a car with the under-engine tray in place :-(
That and "pop down".
One other thing you might want to pick up at Halfords or someplace similar
is anti-seize compound for the plug threads. One assumes that, someday, you
might want to remove them again. :-)
Also observe the tightening torque and you should do just fine.
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