Ken Parker Guitars

[Nick]

^ I'll weld in a piece of thick steel plate with a threaded hole cut in it.

That's what I was thinking Pete. If you have a thread in each plate it won't adjust up and down, the screw will merely move in an out, try it with two nuts (simulating your threaded plates) on a bolt, hold the nuts in a vice or your hand and turn the bolt, the nuts will stay the same distance apart from each other whilst the bolt will move back and forth. You'll need to 'capture' the screw either in the bottom (outer) plate or the upper (inner) one. Personally I'd be drilling a clearance hole in the lower (outer) plate & then turning a deep circlip groove on the screw measuring from the underside of the head up the same thickness, plus a tad, as the plate thickness, then fitting the relevant circlip. That allows the screw to turn freely in the outer plate whilst allowing the inner tube to move up and down the thread. By fixing it to the outer plate the screw head doesn't move which would risk the head protruding out the back of the guitar.