1/. If the Cp, Cpk measurement with verniers can meet 12+/-1mm, then you only need to send us the revised Cp Cpk data. We do not need to change dimension to 14+/-2mm.
2/. If it cannot meet 12+/-1mm, and you need me to widen the tolerance, then we need to change to 14+/-2mm because the lower end of 12+/-2mm (10mm) is too short for our brazing spec. In that case, changing the dimension to 14+/-2mm, you would need to make 30 new samples and remeasure. But this isn’t really a problem because we expect to be ordering another batch of 1500 + 500 tubes from you again in the near future anyway, so this can be part of that.
In any case, we also need Cp Cpk of the internal diameter of the tube as well (8.05).
I hope that makes sense.