Is this another "2 by 4" dimensional issue?...IOW, nominal vs. reality?
I tend to think each mfr has set a reasonable tolerance for the nominal dimension. Sometimes variations in the manufacturing process (draw, extrude, cut, mold, etc.) can account for a few thousandths within nominal. Some plastics will have varying degrees of shrinkage through high-heat processes. Metal extrusion processes will have die wear over time to contend with.
Et cetera, et cetera, et cetera....
If I were making something requiring precise fit/match, I suppose I'd find myself turning, cutting, filing, etc., the part to a precise dimension, checking frequently with verniers/micrometer, to assure dimensional accuracy.
Have you been frustrated/stymied recently in a particular project by this issue? Tell us more.
KD