I recently had to make some modifications to a heat-recovery ventilation system and discovered once I had gotten into the project that the internal components were installed with square-drive screws. I didn’t have any square drivers with me, so I thought about adapting one of the tools I did have in the box. It turned out to be a file.
Most of my files taper to a square section at the handle end, and my assorted files turned out to have quite a selection of square ends. I found one that fit perfectly and used a rugged set of pliers to grip the file just below the teeth to generate enough torque to loosen the screws.
Mark Rosenbaum, Meriden, NH