I wish I could agree with your technique but I have to go on the side of your customer. We use minus pin gauge sets. I'm not exactly sure what the spec is for "minus" pin guages are but as I recall they are 0.2-0.3 mils smaller than the nominal pin diameter. In the case of your example, a 0.039" minus pin passes through with moderate pressure then the hole is 0.039". Hans Rohr p.s. I also make printed ciruit boards [log in to unmask] wrote: > > PCB Suppliers, > Continental Circuits (PHX) generally pin gauges holes to determine the > actual size. Our SOP has been to use a pin > .001 smaller than the bottom of the tolerance. That is, for a .043 > +/-.003 hole we would use a .039 pin. If this passes through > with normal pressure, we say the hole is at least .040 and is in > tolerance. I can't find this technique documented anywhere and have a > customer who disagrees. They use the same size pin as the bottom of > the tolerance. > > How do you measure holes? I could use some support for our method. >