Not quite Simon.
The metal lip to the socket is 16.5mm so the hole is too small for even the socket to fit in properly. I doubt I'll find a smaller socket so enlarging the hole is the only option, and if I'm doing that then may as well take it up to the right size for the grommet...

As I'm not keen on getting a expensive 17.5mm drilling bit it looks like it's Dremmel tool time...