While I'm not a great fan of Apple's regard of their users fixing their own devices, I can offer, what I believe to be, a plausible other explanation. "Why use

While I'm not a great fan of Apple's regard of their users fixing their own devices, I can offer, what I believe to be, a plausible other explanation. "Why use this design, and why use it only on the outside?" It is plausible that it reduces the cost of final assembly on the device. 1: By using rounded "lobes", rather than sharp-profiled edges, they can use a driver with a soft plastic lobes that have no sharp surfaces on them. The lobes are large enough that the connecting material to the main shaft of the tool will provide a desired level of strength. In fact, I would bet that the lobe connecting material thickness was specifically designed to exceed the required torque rating of the screw.* A square receptacle would not be sufficient, as the 90' edges of the tool would quickly wear down, the tool has to present all round surfaces for this to work. 2: By using a driver with no sharp surfaces, and made of a material softer than the enclosure of the device, they reduce the number of scratches made in the surface of the enclosure by workers who will, and I promise you this, miss the screw quite regularly if they don't get it properly torqued before removing the tool. As the device enclosures are often one-piece, milled and surfaced aluminum, the custom tool and screws would likely have less overall cost than a common miss-rate or miss-error level with a metal tool. I would also posit why so many are having difficulty manufacturing the tool, is because they're trying to make them out of metal. If the above happens to be true, I would think the choice of screw design is an act of manufacturing efficiency genius. * - Having had the misfortune of using plastic versions of all of torx, flat, and phillips head screw-drivers, yes, I can say they don't last long.