Christopher Tidy writes:

The blade needs to be at least 3/16" long,
but no more than 25/1000" thick.

The feeler gage sets from the auto parts store have a nice hard feel to
them. Maybe a bit of the 0.025" leaf cut and ground, held in an Exacto
knife handle, would be just the thing, and renewable.

For that matter, I just checked an Exacto knife blade, and guess what:
0.025" thick!

Richard J Kinch writes:

Exacto

Correction, properly named X-Acto here in the USA.

Richard J Kinch wrote:
Christopher Tidy writes:

The blade needs to be at least 3/16" long,
but no more than 25/1000" thick.

The feeler gage sets from the auto parts store have a nice hard feel to
them. Maybe a bit of the 0.025" leaf cut and ground, held in an Exacto
knife handle, would be just the thing, and renewable.

For that matter, I just checked an Exacto knife blade, and guess what:
0.025" thick!

I think an X-Acto blade would be too brittle.
They aren't made for torsional stress.

RB writes:

I think an X-Acto blade would be too brittle.
They aren't made for torsional stress.

I expect they are knife stock which is hardened and tempered, which is
about what you want for a miniature screwdriver. I don't think "brittle"
is the relevant material property.