We discussed fastener drives in the last blog entry, so logically one thing follows. That’s right, today we’re going to discuss head styles and, along with that, what they are most commonly used for.
I am utterly gobsmacked to see how many people on the internet confused “head” with “drive” and say things like “a Phillips head screw” – I am thinking (again) why people would even listen to someone who can’t get something that basic correct. This isn’t even fastener knowledge: it’s dictionary knowledge. You use a screwdriver to drive in a screw: it’s not called a screwheader.
Pan heads are the most common of the rounded heads. They are thicker and less rounded than a round head. Almost all tapping screws are pan head rather than round head. Because it has more metal in it, it is much better when driving at higher torque levels which is why it’s so popular for tapping screws (and self-drilling screws). (Serrations are available as an option when making these screws to order.)
Modified pan heads are only found on framing screws. Instead of the full-height, almost straight side-walls, they are tapered inward. They are often serrated underneath for greater adhesion to the underlying surface.
A round head doesn’t have a distinct “side” like the pan head does. It’s like an upside-down bowl in appearance. It looks better than a pan head to many people. Almost all machine screws are round head rather than pan head; but almost all sheet metal screws (tapping screws) are pan head and not round head. On a socket head screw (and some security screws), the round head is called a button head and it is fundamentally the same thing. (Serrations are available as an option when making these screws to order.)
A truss head is popular because it’s a very low profile, but they are far more susceptible to breaking because the head is so thin. Truss heads come full crown (full contour) – where the rounding is complete and modified crown (where the top is flattened near the drive). The full crown are much better for most uses but are far more costly. Manufacturers tend to provide one or the other, so the user doesn’t get much choice. It’s important to specify which type you want at the time of quotation. (Serrations are available as an option when making these screws to order.)
A fillister head is closer to a pan head. It has very pronounced side-walls and is narrower in diameter than either a pan or round head. They usually fit inside a pre-drilled hole. Many door locks have fillister screws holding them together between the inside and outside of the door. (They’re inside so you don’t see them). They are far less common so tend to be costlier than pan or round heads and limited in availability.
A binder head is the cousin of a truss head. It is wider than a pan head but low like a truss head. They often have some metal dug out under the head around the shank (called an undercut); when used with an o-ring this helps seat the fastener over the sealing ring tightly. They are far less common, so tend to be costlier than pan or round heads. (Serrations are available as an option when making these screws to order.)
A modified truss wafer head is commonly called a k-lathe head. They are smoother on top and have an even lower profile than a truss head, and have a much wider head for a larger bearing surface. It’s akin to having a built-in washer. They are typically only found on K-Lathe screws. On other screws, a pancake head is more common.
A round washer head is similar to a k-lathe head and is typically found on particle board screws. If you examine the photos, you will see they are quite different than the modified truss wafer head. The round washer head is higher because it’s a round head with a washer built in, whereas the modified truss wafer is a truss head with a built-in washer. The washers come in various outside diameters when being made to order.
A pancake head is usually found on clip screws, but they also can appear on machine screws and tapping screws. They are perfectly flat – picture a nickel placed flat across the screw shank. While these are flat heads, they are not countersunk.
A flat wafer plymetal head is typically found only on plymetal self-drilling screws. They have a flat pancake-style head with a separate countersunk part under it. The head has a lip between it and the countersink.
A sidewalk head is usually only found on machine screws and those machine screws are called sidewalk screws – some people call them sidewalk bolts but they are not bolts. They are a cross between a pancake and truss head, and originally were purpose-designed for one thing (moving sidewalks, hence the name). Due to the thin profile, they only are available in slotted, Phillips, or slot/Phillips. Other drives over-torque the part and the heads pop off.
Wing screw heads are found only on wing screws. It’s a head that looks like a wing nut. These are designed so you can screw them in or out by hand with no driver.
Thumb screw heads come in different varieties (some of which are pictured) but they serve the same purposes as wing screws. The knurled thumb screw, for instance, is commonly used in electronics applications.
Flat heads are designed for countersinking when you want the head flush with the surface. You have to countersink the hole (not always – see next entry) prior to installing the screw. Flat heads in the United States (and most of Canada) are almost always 82° angles under the head except for military and aerospace fasteners which are usually 100° -- metric fasteners are typically 90°. Some flat heads are undercut because of clearance issues in the underlying material or surface; they may also be undercut when the fastener is very short to provide an extra thread for proper engagement.
Flat heads with self-countersinking nibs are designed for countersinking without the need to countersink the hole first. These screws are for particle board (primarily) and other soft woods. You have to countersink the hole (not exactly – see next entry) prior to installing the screw. Particle board screws are almost always 82° angles under the – some metric versions may be 90°. You cannot put nibs on an undercut screw so none of these parts are undercut.
An oval head is a flat had with some doming at the top. They provide an attractive, finished look and are very popular in the marine industries where they sometimes want the fastens to be noticed as part of the design. Like flat heads, they come in regular and undercut. Oval heads in the United States (and most of Canada) are almost always 82° angles under the head except for military and aerospace fasteners which are usually 100° -- metric fasteners are typically 90°. Some oval heads are undercut because of clearance issues in the underlying material or surface; they may also be undercut when the fastener is very short to provide an extra thread for proper engagement.
Bugle heads are typically used in drywall (gypsum board) to hang the drywall or attach something to the drywall. They are flat heads that are curved (bevelled) so they seat into the drywall without any pre-countersinking and with minimal tearing to the surface of the drywall. Then they can be covered over as they are flush with the surface. Bugle heads come with either a self-drilling point or a self-piercing point. In rare instances they may come with a spoon or spade point.
A trim (reduced) head screw is when the head is smaller than normal (normal being defined as what the IFI/DIN specifications state). Any screw can be offered as a trim head. For example, a #8 screw with a #6 head is said to be trim (or reduced). You have to specify the head size, though typically the next common size down is used. The chart pictured right shows the standard screw size (“size”) and what the most common reduced size is (“trim”) and the less common head size (“trim alt”) if it exists. Any head can be made trim, but tooling charges may apply.
Cylinder heads (usually with knurls) are typically seen only on socket cap screws. Without knurls, they are very similar to fillister heads and used primarily on bespoke screws for furniture and door hardware.
Confirmat heads (sometimes called Euro Heads) are found on special European furniture screws. The head is very tiny (height- and widthwise) for the screw and a 90°-degree angle. They are always on metric-sized parts. The head is the same as the Euro Screw head though because the screws look so different people often don’t believe it until they see a picture of only the heads side-by-side as pictured to the left.
Acoustical heads are primarily used in overhead applications and designed to be used with a wire going through the eye. The name comes from the acoustical ceiling tiles common in many offices where it was originally used.
Hex heads are popular because you can put them in with an impact driver as well as a standard nut driver, or even a standard screwdriver. Many different drives can be added to a hex head (or combinations of drives). They come with and without washers. The heads can be indented or not. They can even be domed (those are usually used in appliances). Some are encased in a rust-resistant cap (casing) usually made of stainless or Zamac alloy – and the capped screws can even have an EPDM washer under the head for sealing purposes. The hex integral washer is different than the regular hex washer because the integral washer is on a tapered angle instead of a flat washer – these often are used with a sealing washer (though in this case it must be just the sealing washer and not the bonded sealing washer).
Obviously, we can make anything for you at Hardware Everywhere. If you want a #9 screw with a #7 head that is 1-7/16” long with a 90° oval undercut and nibs coupled with a type-U knurl on the shank made out of an exotic alloy, and don’t mind waiting we’ll get it made for you with an appropriate minimum order quantity. You can get the exact fastener you want for your application.