Right, the bullet has been bitten and I took a hole saw to my lovely new guitar body and we now have provision for stereo and mono jack sockets.

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The retaining plate (or whatever you want to call it) I made from a bit of a scrap pickguard just to try the idea.
I was surprised at how stiff it was but a quick dunk in some boiling water and it curved nicely.
Its a bit thick though and I'd really like to make a recess for it to fit flush but I might just end up chamfering the edges so it looks better.
The finished article will match the new pickguard and pup ring that I am making in pearlescent black.

Quick question while I'm here - I know what I need to finish with but what grade grit is recommended to start sanding with?