In article ,
P.J.Leon wrote:

I want to use these bits for reference drilling.Some times I have to
run
telco and network wiring between floors.I have 1/4"x18" wood bits but
they leave a good size hole on the floor.As you see,wood is the
material
that I have to drill thru.I found a place that sells drill blanks that
are even smaller than 1/8.

The people who installed air conditioning ducts in my house used stiff
pieces of wire with a crude tip. Must have been cheap, they had them in
bundles and quite a few bent and were discarded but most went thru and
were left in place so they could measure from both sides.

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