This month we agreed a price with a customer on a washer 1.60 mm thick. Their drawing said 1.80.
Point two of a millimetre sounds like nothing. On a die cut washer the material is most of the cost, and the material goes up roughly in a straight line with thickness. 1.80 divided by 1.60 is 1.125. So the thicker washer uses about twelve and a half percent more sheet, on every piece, for as long as the part runs.
On a small order nobody would notice. On a part that runs to lakhs of pieces a year, it decides whether the job is worth doing at that rate.
So the rate went out in writing against 1.60, and we asked them to confirm the thinner washer works in their assembly. If it does, they save money every month. If it has to be 1.80, the rate changes, and better we both know that now than when the first invoice arrives.
When a supplier asks whether a thickness can change, it usually is not fussiness. Somebody has done this sum.