All I can figure out is that engineers who decide what type of fasteners to use in equipment are either sadists, or own stock in tool companies. Why else would they keep changing the heads on screws and bolts used to fasten together farm equipment?
I was comfortable with conventional slotted screws, Phillips head screws and Allen head screws. I accepted their downsides. Slotted screws were prone to stripping out the slot. The heads of Phillips-head screws and Allen head screws would take more torque, but once you stripped them out there was nothing left to do but drill and dig out the mangled screw.
Then they started using screws with "hexalobular socket heads," also known as "star drive heads," most commonly called "Torx head " screws. I fretted and mumbled, but eventually bought a set of Torx-head screwdrivers and a Torx-head sockets, and now reluctantly admit they tend to resist stripping-out better than the old-school screw head designs.
But darn it, this week I ran across yet another design in screw heads, a fiendish variation called the Pozidriv, a trademarked design very similar to the good old Phillips-head design. At first glance Pozidriv screws look like Phillips head screws, but on closer examination have tiny indentations, cuts or lines between the cross where you place the tip of the screwdriver. A Phillips head screwdriver will work--sorta--in a Pozidriv screw, but not as well as a Pozidriv-tipped screwdriver. A Pozidriv screwdriver in a Pozidriv screwhead is a pretty tight, precise fit that withstands a lot of torque. Using a Phillips head screwdriver in a Pozidriv screwhead may work, but will likely strip out just about the time you really lean into tightening it.
Bottom line: Yep, I bought a set of Pozidriv tools this week. It's a cheapie set, a screwdriver handle with interchangable tips. But this time I fooled the engineers--this set has screwdriver tips for every imaginable type of screw head. It's got slotted head, Phillips head, Pozidrive, Allen head, Torx head, Robertson, Security, Torq-set, Spanner Head, Double Square, PolyDrive and other screw head designs that I've never seen or heard of.
But just watch--next month all the trade magazines for mechanics will trumpet the introduction of a revolutionary new screw head that won't match up with any existing screwdriver.