To facilitate easier mounting of the string locks, especially with necks that are radiused beyond the nut and for e.g. 7-string guitars with truss rod access, it makes sense to mount the string locks on a plate and mount that plate on the neck. I have made a few of these for my own builds, but can also offer as custom projects made to specification.
Here are three freshly made for luthier Rick Canton, each tailored to exact measurements of the tapered neck width of some of his on-going projects (from top to bottom: Al Schaffer, Tim Miller, Allan Holdsworth), on their way to the anodizer for black finish:
I generally make some spare each time I rig machines up, either for custom hardware or complete instruments.