If a test procedure is verifying all dimensional accuracy, it can be assumed to be bounding tolerance. If it's a mass production line with less than 100% testing of parts, you'd have to expect that some outliers get by and the tolerance is something like 3-sigma on a Gaussian.

Yeah it's probably field specific and I guess Gaussian-based uncertainty would be more about statistical sampling rather than tolerances. I've noticed that if arithmetic is being done on it it's almost certainly Gaussian. I just mean whenever I see uncertainty like this, I don't know what is meant!