The flathead screwdriver I get (it’s the simplest, and the first one people came up with).
The Phillips head screwdriver I get (quicker to fit head into screw slot for use with powerdrivers/for mass assembly).
But after I just had to buy a T20 torx screwdriver to repair my chainsaw, I have to wonder what the point of a six-sided, non-tapered (a la Phillips) screwdriver is.
Likewise, square drive. My carpenter friend briefly mumbled something about less risk of stripping … true?
From some things that I have read, new screw designs have been driven by things such as speed of assembly, control over torque, cost of screws, and compatibility with power tools.
I’m sure others will be along with better answers, but…
Torx, specifically, can withstand a much higher installation torque (get it) than slotted or phillips without camming out. Basically an improvement on the hex recess used in socket screws, and quicker (IME) to get the bit into the screw.
The square drive (Robertson) doesn’t strip easily and holds the bit much better than Phillips or slotted screws. Phillips screws are actually intended to pop the bit out after a certain torque. But given that modern drill drivers have clutches that allow you to set the torque, this is no longer such a desirable feature. A lot of woodworkers and carpenters (especially deck builders) really like the square drive screws because you can drive them without pre-drilling without worrying too much about stripping the heads.
From what I’ve learned over the years in working on boats.
The slot drive just doesn’t lend itself for power screwing. Obviously.
The Robertson or as you say square drive has been around in Canada for decades. In my opinion this is the most superior, requiring very little push when screwing. It is the least likely to strip.
The Phillips is ideal for a high production environment where little torque is required. The bit very easily and quickly slips into the screw head , but if you need to apply torque you sometimes have to push hard. The automotive industry uses this system extensively, since most applications involve sheet metal. But the screw heads easily strip under heavier torque.
The Torx and Hex head attempt to provide the benefit of the square drive. I’ve had very little experience with the Torx, but having used the Allen keys quite a bit I can tell you that the Hex head easily strips the screw. Stands to reason as the cross section of the bit is way more rounded than the Robertson.
With kitchen cabinetry, the square drive hardened trim screws are the cat’s pants. By taking off the doors and drilling/screwing them together, a run of cabinets will stay perfectly aligned and tight no matter what. Although I’ve snapped a few, never had one cam out or strip.
When I was fixing equipment in the military, almost all of our equipment used torq-set screws. At first glance, they look like phillips screws, but if you look closely, the blades are offset from the center. They were much more durable than phillips screws, easy to use, and easy to torque to a specified value. In our maintenance manuals, almost every screw had a torque specification. I’ve often wondered why they weren’t more widely used in commercial hardware.
To answer the OP more specifically, all these newer styles we’ve mentioned (plus the Pozidriv) have the walls of the cut into the screw head to be vertical. The older style slotted and Phillips heads have sloped sides. The advantage of sloped sides is that pretty much every Phillips screwdriver fits every Phillips screw head (within reason), but the disadvantage is that when you crank down on it, the sloped sides mean that the torque tends to push the driver out of the head. It’s an inclined plane, on its side.
Vertical-cut screws don’t cause the bit to slip out, so it’s easier to apply more torque.
The Robertson (square) head screw and driver do not have parallel sides. There is a small taper to this design which facilitates inserting the driver into the screw head more easily, but also to create a positive grip on the screw which facilitates single-handed operation. The Robertson head allows one to place a screw on the end of the appropriately sized driver in any orientation (even vertically underneath the driver - although not consistently in this position), and then use a single hand to maneouver the driver and screw combination into position.
FWIW when our car factory changed over from Phillips to Torx I was told that there was a saving of $5,000,000 USD. This was money that was previously spent when Phillips screwdrivers sliped out and damaged other nearby parts. :eek:
It was mentioned that some screw heads are there to reduce vandalism. You have the entire concept of a “one-way” or “permanent” screw to back this up. On the screw head there are only “walls” to hold the driver when tightening the screw, if you want to loosen the screw, your out of luck, as the driver has nothing to press against, and just rotates out of the screw entirely.
-I knew of these screws, but just saw one for the first time recently. Is it wrong to think that if you can grip the entire head (that is around the head instead of the slot so designed) you can indeed unscrew a one-way screw?
When I worked on the Lockheed L1011 most of the panels were fixed with Tri-Wing screws. We were told that because of the profile of the detent in the screw it had more of a bearing surface to remove a screw than to fit it, thus making it easier to remove. Oh yeah.
Yes, if you can grip the entire head it will back out like a normal screw. I’ve seen a special tool that pops the head off then the screw body is removed.
Tamper resistant torx or hex drives have what looks like a nib in the center. Requires yet another set of wrenches that have a hole drilled in the end of the tool.
Not stuff you will probably find a Sears, but they’re out there and easy enough to find.
We called these “swastika” screws when I was working on F-14s but the only place I recall them being used were for waveguide connections in the radar.
F-14s used panel screws in some places that had a shallow coin shaped slot that was easily stripped, presumably to prevent it from being tightened too much. Paint and a bit of corrosion would commonly cause the screws to strip when removing so they often had to be drilled and remved with a broken bolt extractor.