Ponder the humble screwdrivers that live in a typical kitchen junk drawer.

Some are used for probing. Some are used for prying. Some are used for scraping. Some are used for chiseling. Some are used as can openers.

…But some are actually used for loosening or tightening screws.

Never use a screwdriver as a crowbar, use a dedicated set of pry bars instead.
Same goes for scraping gaskets too, there are special tools for these jobs.

(Image/Wayne Scraba)

But improper use of a screwdriver has its shortcomings. Aside from the potential to hurt yourself, a damaged screwdriver will often be spoiled from ever using it for the intended purpose.

Here’s why:

The overall size of the screwdriver is the length of the shank (shaft) in inches. A six inch screwdriver has a shank that is six inches long, a four inch screwdriver has a four inch long shank, and so on. That’s easy, but the blade widths also vary, and they can vary within the various lengths. The tip of the standard flat blade screwdriver must fit the screw. Typically, the tip of the standard screwdriver blade must be equal to the width of the head of the screw.

If the blade is too large, then there’s a good chance it will not be able to enter the slot of the screw completely. This can (and often does) damage the head of the screw as you attempt to turn it. If the blade is too small, it too can damage the head of the screw. It can also damage the screwdriver tip.

The good news is, there are plenty of different screwdriver sizes and styles out there.

Obviously, a screwdriver with a long shank allows you to get at hard-to-reach screws, but they can come in handy for other jobs too—like adjusting old motorcycle carburetors while you’re sitting on the bike.

Of course, not all screw locations allow you to use a super long screwdriver. Sometimes, all you’ll have room for is a stubby screwdriver. Stubbys are available in several different configurations with the most common automotive jobs in standard flat blade and Phillips.

The blades of a quality screwdriver are usually machined so that they are parallel to the shape of the slot in the screw. Many quality screwdrivers have hardened tips. This obviously extends the life of the screwdriver.

Some screwdrivers are manufactured with a square shank. Others have a round shank. The square shank allows you to use a wrench on the shaft for added leverage.

Better still, a few screwdriver manufacturers even incorporate a hex into the shank so you can slip a box-end wrench over it. Many screwdriver handles (Craftsman comes to mind) are designed to accommodate a large wrench too.

In automotive applications, the most common screwdrivers are the standard flat blade, Phillips head and Torx head. The occasional application makes use of a clutch head screw (sometimes called a “butterfly”).

Typically, the Phillips screw (a trade name) incorporates two slots that form an “X” on the screw head. The design allows you to apply more torque to the screw without damaging the head. Phillips screw heads have an internal taper. The number one Phillips screwdriver has the most pointed head. A number two Phillips is less pointed and so on through to number four. Most often, the larger the screw, the larger the screwdriver tip number.

Torx head screws incorporate a six-lobe star-pattern. Originally, they were designed to fix an issue with Phillips screws. The Phillips has a tendency to “cam out.” This means the screwdriver can slip out of the head as torque is applied. With repeated use, this tends to damage the screw. Torx head screws are engineered to prevent this. Basically, the design allows you to apply more torque to the tool and consequently, the fastener. When determining the size of a Torx screw, smaller numbers indicate a smaller head size. Most common, you’ll find T10, T15, and T25 screw heads. Metric and inch Torx fasteners share the same screwdrivers.

Roberston or square drive screwdrivers are more common in woodworking than in the automotive field. Typically, the allow for single hand operation. They also allow for more torque to be applied when compared to flat or Phillips head screws.

There are a handful of other screwdriver types suited to specific jobs too, including offset Phillips screwdrivers, magnetic tip screwdrivers, precision tip screwdrivers (often used for tiny electronic applications), and so on.

As you can see, there’s a lot more to the humble screwdriver than first meets the eye. And yes, it’s easy to mess up by mistreating a screwdriver, but if you use the right tool for the job, a good quality screwdriver can last a lifetime.

The most common screwdriver is the flat blade. As you can see here, they come in all sorts of sizes and lengths. (Image/Wayne Scraba)
The size of the screw determines the size of the screwdriver. Typically, the blade is machined so that they are parallel to the shape of the slot in the screw. (Image/Wayne Scraba)
If the blade is too large or too small, it can damage the screw. (Image/Wayne Scraba)
The next most common automotive screwdriver is the Phillips. Like the flat blade, there are all sorts of different length and size combinations. (Image/Wayne Scraba)
When it comes to Phillips screwdrivers, the number one Phillips has the most pointed head. A number two Phillips is less pointed and so on through to number four. Once again, the size and shape of the screw determines the screwdriver number. (Image/Wayne Scraba)
These two super long Phillips screwdrivers are more useful than you might first think. The added length allows for added torque to be applied to the screw. (Image/Wayne Scraba)
Look closely at the tips of these screwdrivers. The tips are hardened. Not all screwdrivers have hardened surfaces. (Image/Wayne Scraba)
pair of mac screwdrivers with wrenches for more torque
Another handy feature that a few screwdrivers have, is a hex on the shaft. This allows you to use a wrench to add torque when tightening or loosening the screw. (Image/Wayne Scraba)
Another screwdriver type you often encounter in the automotive field is the Torx, AKA “star.” (Image/Wayne Scraba)
Close up, you can see it consists of a six-lobe pattern. This allows for more torque to be applied to the screw. (Image/Wayne Scraba)
Occasionally, you’ll encounter a square tip “Robertson” screw. Typically, these are found in woodworking and see little automotive use. Like others, Robertson screwdrivers come in various sizes for various screw heads (Image/Wayne Scraba)
Stubby screwdrivers are extremely useful. They’re available in pretty much every style you’d need. (Image/Wayne Scraba)
A bit driver set such as this can come in handy. Mine doesn’t see much use, but as you can see, it includes a wide range of tips—even seldom used “Pozidrivs,” which are similar to a Phillips, but the screw has four extra notches to prevent cam-out. (Image/Wayne Scraba)
Remember when we said screwdrivers are often improperly used? This is what can happen. When used for prying the tip can break. (Image/Wayne Scraba)
pry tools on a workbench
Instead of using a screwdriver as a pry tool, try one of these dedicated pry bars. They work better! (Image/Wayne Scraba)

Keywords
Screwdrivers, Tools
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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.