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Screws are everywhere. They hold your life, and your furniture, together. Screws come in all different shapes and sizes but chances are you’re probably only familiar with a few of them. There’s Phillips and flathead, and—if you’re from Canada—the square Robertson screw as well. But that is only the tip of the screwy iceberg.
Here is a brief tour of some of the more exotic ones.
The Mortorq screw was built by the Phillips Screw Company, and there is a resemblance between it and the company’s signature screw. The main advantage the Mortorq screw offers is, as the name implies, more torque. Specifically, the wide wings of the screw make for thicker and stronger drill bits, and the increased contact area means more force is applied to the screw. Essentially, this is a heavy-duty Phillips screw, commonly used in automotive and aerospace work.
You may have some pentalobe screws lying around if you own an Apple device. Pentalobe screws were first implemented by Apple in 2009 on its Macbook Pro battery cases. Since then, they’ve been implemented externally on several Macbook models, and on every iPhone since the iPhone 4.
The primary purpose of pentalobe screws is essentially just to be obscure, so you won’t automatically have the right screwdriver to fit them. It’s a move to curb tampering and fiddling with Apple’s characteristically closed devices. Although, now that Apple puts them on everything pentalobe screwdrivers are pretty easy to find.
One-way screws come in all kinds of different shapes, but they’re all used for the same purpose: turning one way and one way only. Typically, these screw drives are designed to fit slotted screwdrivers, and feature a gentle slope in one direction that provides zero torque. They’re commonly found in public restrooms and other places where people shouldn’t be unscrewing things.
Lox screw drives have the shape of four overlapping squares. The idea behind this type of screw is to increase the number of contact points, which increases torque and decreases wear. Lox screws have twelve contact points, one for each side, many more than the four contact points on Phillips or Robertson screws. This makes Lox screws well-suited to high-torque applications in industry.
At first glance, this looks like a typical Phillips screw. However, there are many important differences. The Frearson shape is a perfect cross, unlike the rounded Phillips cross, giving the Frearson screw higher torque and preventing the bit from slipping out or stripping the screw. Further, the walls of the screw drive are designed so that a single screwdriver can fit every size Frearson screw. Basically, Frearson is like a better-designed Phillips.
Pozidriv is another screw designed by the Phillips Screw Company. Like the Mortorq screw, the Pozidriv is designed to provide a greater contact surface for more force and less slipping. One of the biggest downsides to the Pozidriv is that it looks too much like a Phillips, and people often use a Phillips screwdriver on a Pozidriv drive, or vice versa.
While the two are slightly compatible, they’re not as effective and using the wrong bit can severely damage either the screwdriver or the screw. The best way to tell the difference between them is that a Pozidriv screw will have a small, shallow secondary cross in between the main cross.
Torx screws were invented in 1967 as an alternative to the already popular Phillips screw. Torx drives feature six (or sometimes five) lobes, and this greater number of lobes increases the contact surface considerably. As a result, Torx screws can bear greater torque and slip out less easily than Phillips screws. Torx screws are used in all manner of applications, primarily in the automotive and electronics industries.
Torq-set screws are designed by the Phillips Screw Company for sensitive aerospace applications. The goal is to create an extremely high-torque screw. Every part of this screw design—from the straight walls to the offset cross—is intended to provide the greatest possible torque. Perhaps the most famous application of Torq-set screws is in holding together the B-2 stealth bomber.
TA and TP3 are two different types of screw drive, but they look fairly similar. They’re triangular drives, which is fairly unique. The TA has straight walls, while the TP3 has walls that curve. You’ll often find these screws in the toys in your Happy Meal, and the TA is also used in a bunch of low-security applications like elevators and camping stoves.
It’s not hard to find a screwdriver that’ll fit it, but it’s not super easy either, which is just enough security to keep people from opening up a stove and accidentally making it explode.
The Tri-wing screw is another Apple screw. It was used in a few Macbook Pros back in 2010 and 2011, and it’s also holding stuff together in the new iPhone 7 and 7 Plus. This one isn’t proprietary though, and it can be found in products made by Microsoft, Nokia, Nintendo, and others. In the past, the Tri-Wing was mostly used in aerospace, and can be found in some old aircraft made by Lockheed and McDonnell Douglas.
Key-Rex screws are used in high-security applications, like ballot boxes and bank vaults. Key-Rex screws are custom-made with a unique shape that can only work with the corresponding unique screwdriver. Essentially, Key-Rex screws are unique keys, deliberately created to be impossible to unscrew for anyone without the corresponding driver.
This article first appeared on Popular Mechanic.