SpaceTEC’s Overview on Screwdrivers and Screw Heads

Greetings, avgeeks!

I received some encouraging feedback from my last post about SpaceTEC so I figured I would serve up another helpful short clip. Instead of safety wires, this brief guide covers the basics about screwdrivers:

Of all hand tools, screwdrivers are among the top in terms of popularity and usefulness. And yet they are not complex devices that require a PhD. As SpaceTEC states as a running footer in the above clip, screwdrivers offer simplicity when it comes to applied mechanics; they are made for the sole purpose of loosening or tightening screws. Nothing hard to understand there.

Search for a screwdriver and your head might get all twisted up since there are a variety of types—everything from slotted to jewelers. So how in the heck do you choose what is right for your application or assemblage?

According to SpaceTEC, screwdrivers are “classified by shape, type of blade, and blade length.” They recommend selecting the largest blade (or bit) that will fill the screw head. This makes sense. Why? If you’ve ever tried to fit too large of a bit into the head, you know that it obviously won’t work. Neither will trying to place a bit too small into the screw head. They won’t fill in the hollow correctly. They also won’t effectively turn the screw. Instead, a bit that is too small or too large for a socket will warp and misshape the screw head so that the right blade won’t even work. Oh, and it can even damage the bit itself. Talk about a frustrating and costly blunder.

The two most well-known screwdrivers are the straight/common/ flathead (which fit with slotted head screws) and Phillips head (which fit in heads that form perfect crosses). There’s also offset screwdrivers that have a Z-shape and are composed of two right angles that are designed for use in hard-to-reach areas. Offset screwdrivers can have tips that are either common or Phillips or both.

To select an appropriate screwdriver the main issue revolves around the screw head. Therefore it is really the screw that determines how to select the right driver. SpaceTEC lists nine screw heads, which are briefly identified below:

Slotted – The most basic type. Can’t get any simpler than this design and in fact it is probably the oldest and cheapest to make. A straight vertical or horizontal (depending on your position) line down the middle of the head.

Phillips – Perhaps the most famous. Try and not find this type of screw head. It’s certainly a household screw. Its cruciform shape allows for better torque.

Pozidriv – Nope, that is not a misspelling; the Pozidriv (which may or may not be derived from the term “positive drive”) is another cruciform type head. However, it almost looks like it is a “bloated” cross, i.e. kind of widened in the mid-section. An advantage over its predecessor: it has straight flanks as opposed to the round flanks of Phillips. This helps prevent what is referred to as “cam out,” i.e. that accidently and incredibly frustrating time when the screwdriver slips out of the screw head.

Torx – Also known by its less appealing, technical name “hexalobular.” This recess is designed to resemble a star with six points. This allows for greater torque while resisting the tendency to cam out. That results in less fatigue on your hand but also prolongs the life of the bit on your screwdriver.

Hex – Short for hexagon, it has a six-sided polygonal shape. It is specially designed for use with Allen wrenches (or “keys”). The advantage here comes with size: Allen keys can fit and rotate in smaller areas where other screwdrivers can’t.

Robertson – A good way to know this screw head’s advantage is by remembering this: “Robertson retains.” It has a square-shaped socket (indentation or recess). Its tapered design offers reduced cam out and product damage while speeding up production. This type of head is used prominently in Canada.

Tri-wing – As the name indicates, this screw head has a triangular recess with three wings extending from the vertices of the triangle. This socket was particularly designed for use in aeronautics but has since been extensively used for electronics equipment in other industries.

Torq-set – Another cruciform. Don’t adjust your glasses, this socket looks similar to a Phillips head but something seems off. Actually, that’s it—while it has a cross-shape, the “arms” are offset as if the lines were broken up. Thus, a Phillips screwdriver will not fit. This screw head is used in aviation.

Spanner – This screw head consists of two round holes that look like a pair of eyes. This design’s main purpose is to prevent tampering.

If you’re an avgeek, chances are you already know about screwdrivers and screws. Still, brains are like machines. Just as machines often need to be well-oiled, frontal lobes need lube in the form of learning and re-learning. Reinforcement is, after all, a major component in keeping things structurally sound and operational.

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About Sandy

Nuts and bolts and anything in between. Yeah, I know plenty about fixing aircraft. I aim to be the best mechanic. Hanging out all day in a hangar sounds like a perfect use of my time. You got questions pertaining to maintenance and repair? Ask away and I’ll have you flying high. If not, check some of my posts for tips or suggestions on what parts and supplies work best.