What you are looking at is no ordinary screwdriver. This is Z.I.M.S - Zuffenhausen's Incredible Missing Screwdriver! This is the screwdriver Porsche failed to put in your tool kit!
"Why?" You ask.
Well, we're not sure why they didn't, but we do know why you need it.
Allow us to explain -
It has been years since the correct screwdriver has been available to hold the inner pulley of the 356/912 (and VW) while removing the nut to adjust or replace the fan belt. In order to properly function, the blade of the screwdriver must be parallel to the shank. This allows the tip of the blade to rest on one of the two screw heads that hold the generator together, and the shank to fit squarely in the notch on the inside pulley.
The Z.I.M.S. has heavy chrome plating on the blade and shank and an insulated plastic handle for durability.
If the inner pulley notch has been distorted and does not have a sharp square hole, this should be replaced. The screwdriver cannot compensate for a worn pulley.