On Fri, 14 Nov 2003 12:03:37 -0500, "surftom"
wrote:

How do I *accurately* (n.nnnn) measure very small hole diameters?

I can poke them with a numbered drill but that would only get me close by
"feel" and only if the hole was a standard size. e.g. measureing a .0431
hole is kind of hard with a vernier or mic

No real reason - enquiring minds just want to know

Tom

Gauge pins can be bought in .00005 inch increments. Deltronic makes
them. Also, air gauges and their electronic counterparts can be used.
Air gauges work by letting air out a hole. This relieves the pressure
some what in the system. This pressure either moves a dial or floats
an indicator in a graduated tube. The hole in the gauging member will
be close to the inside of the hole. If the hole is the same size as
the gauge then the pressure will be high. If the hole is much oversize
then the pressure will be lower because the side of the hole will be
farther away from the hole in the gauge thus letting more air out.
There are other ways as well.
ERS