I designed this thing when I got tired of my standard flat-head screwdriver slipping out of a multi-turn potentiometer on small SMPS boards. This design encloses the flat head in a circle just a little oversized for the pot's adjustment screw. The design also has two shoulders on the shank so you can align the flathead blade. This was designed to fit the iFixit Precision Screwdriver set, but should fit an 4mm driver.