You indeed need a 16mm AF socket with an outside diameter of approximately 22,6mm, otherwise it won’t fit inside the sparkplug tube.
I have been using a Mercedes tool for this (Gedore Nº58), fits perfectly.
And I could get it cheap of course [:D]
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<font color="blue"><i>1980 TR7 DHC (my first car, now restored and back on the road)
1981 TR7 FHC Sprint (better known as 't Kreng)</font id="blue">
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