I think I remember that there is a kind of "touch indicating paper".
If you are uncertain whether two surfaces touch when an assembly is assembled, you can put some of this paper on one of the surfaces, assemble the assembly, disassemble it, and if the touch-indicating paper has changed colour, you know that the two surfaces did touch.
What is this kind of paper called, where can I get it, and does it only work for metal surfaces, or does it also work for wooden surfaces?
Michael Bell