... chairs may be the way to go, even if used functionally as the rail fixing. That way -- a) it is self-adjusting for the rail width, and b) there is no need for the dreaded chair threading. It is not really practical to use injection-moulded chairs as functional half-chairs because of the large hole in the base needed for the tooling pegs, and the difficulty of cutting them off-centre under the key. But it would be fine if they are 3D printed: 2_120417_270000000.png It takes only a couple of seconds to bend up a paper-clip to make a rail clip, and once you have made a boxful they are re-usable. The inner half-chairs could be clipped to the rail while it is glued in position and to gauge. When set, the clips are removed one at a time and the outer half-chairs are added. No I haven't actually tried it. But if I was experimenting it would be the first thing I would try. It may take ...