In article op.xj80ztko2cx0wh@ajm,
RobertMacy wrote:

you need a 'tiny' metal detector! A small version of those things people
scan around over the ground, but only 1/2 inch in diameter. I've got one
with a 1/4 inch diameter in my lab. If you want a LOT of details, contact
me offline. From memory it can 'see' a nail something like 6 inches away.
or was that a foot? can't remember now.

you can make one with some effort. A coil and your soundcard. Power the
coil with the soundcard drive while monitoring the 'response' of the coil
with the input of your soundcard 'listening'. Then moving the coil around
on top the bench will find stainless steel as well as ferro iron
screws/nails.

If Perce's swiveling-magnet nail finder won't find them, they may be
brass screws. Either way, the metal detector approach may be the best
way to find them.

You can build a simple oscillator circuit that operates near the
frequency of a local AM broadcast station. You would use the
oscillator's coil as a probe to detect metallic objects, assuming it is
an air-core coil.

You would tune the oscillator to produce a whistle when listening to the
station on an AM radio. When the coil gets close to a metal object, the
whistle pitch will change. Use the lowest pitch you can hear for best
sensitivity.

I have not tried the sound card approach, so do not know how sensitive
it may be. It should be easy to try with two coils of wire, if you know
how to generate and detect a tone.

Fred