Types Of Screws | Albany County Fasteners

Types of Screws

Screws are a fastener variety that is widely used every day. They come in many shapes and sizes and all have different uses depending on the type of screw. The word screw and bolt are often used interchangeably. You will often see smaller fasteners called screws and as they get bigger they are referred to as bolts. Generally, the term screw defines any fastener that after being installed into the material holds itself into that material. A bolt is used to bolt two materials together by going through the materials and being fastened with a nut, creating a bolted joint. Consider that a machine screw needs a nut or a pre-tapped hole to install.

Screw Terminology

Screw Terminology Diagram: Drive Style, Head Type, Shank, Threading, Point, Diameter, Length, Threads Per Inch, and Thread Pitch

Material: The material that a screw is made out of. Often chosen based on environmental and structural needs.
Grade: Different compositions of a material that can change it’s qualities, making it a better choice based on environmental and structural needs.
Diameter: The thickness of the over-all screw. Determines the size of the hole that needs to be drilled into the materials.
Length: How long a screw is. This measurement can vary depending on the head style of the screw.(See Helpful Resource #2)
Threads Per Inch (TPI): Amount of thread peaks measured from peak to peak in an inch length of the fastener. Used to measure threading for imperial fasteners.
Thread Pitch: Distance between two thread peaks. Used to measure threading for metric fasteners.
Drive Style: Indicates the type of driver to be used for optimal results. For example: A Phillips head indicates a Phillips driver should be used.
Head Type: The top portion of the screw and contains the drive style. Screws have different head types based on the application they are being used for. Some make the screw flush with the installation surface while others leave the screw head exposed for a quality finish.
Shank: Refers to an unthreaded portion under the head of several types of screws. This can vary based on the length, diameter and type of the screw. The shank aids in compression and clamping force of the installaton materials, as well as, reducing the chance of breaking due to over-heating.(See Helpful Resource #1)
Threading: The portion of the fastener that has a helical shape rolled into it. Causes the screw to pull into the material and hold in place.
Point: The very tip of a screw. Depending on the type of screw, a variety of points can be available. For example: Drill Point, TEK Points.

*Note: A drive style usually has several different sizes as well. Usually indicated by a number for example: Phillips #2

Measuring Screws

Screws are measured in diameter by length. An example of an imperial screw measurement would be a #7 x 1″ deck screw. The #7 is the pre-defined diameter of the screw and the 1″ is the length of the screw. Imperial diameters range from 0 to 24 and their lengths are measured in inches. When measuring a metric screw, you use the same format of diameter by length, but both are measured using millimeters. For example, an M5 x 10M means a diameter of 5mm and a length of 10mm. It is not uncommon when dealing with screws to see the thread pitch added in as well.

Imperial	Metric
1/4″-20 x 1″	M5 x .8 x 10M

As seen above, the thread pitch is added into the middle. For imperial the 20 stands for 20 threads per inch whereas with the metric the .8 stands for .8 threads per millimeter. It is common practice to leave out the thread pitch on screws during the listing process as the pitch matters less because it does not have to match a nut. When measuring the length of screws, the head of the screw will matter. For most screw types you measure from the bottom of the head to the tip. An exception to this rule is a flat head. Always measure flat head screws from the top of the head to the point.

Screw Installation

Installing screws is a simple process. Using either a screwdriver or drill/driver with the appropriate driver bit, place even pressure on the drive recess and being spinning it. The way you will need to spin depends on the orientation of the screw threads although most are right-hand threaded (meaning spin to the right). Some screws have self-drilling points which are essentially a notched tip that allows a screw to drill into the material as it is being installed. Wood screws should always have a hole pre-drilled before installing them. Pre-drilling into wood will prevent cracks and splintering from occurring especially when working with hardwood. Self-tapping screws have sharp cutting threads that will cut deeply into the material during installation for a more secure hold.

Types of Screws

Screws are all engineered for different purposes. It is best practice to use a wood screw for wood for example because it was designed to have the optimal hold in wood applications.

Concrete Screws

Concrete Screws are easily distinguished by their blue coating which protects them in harsh conditions. They cut threads into concrete and are used to secure materials to concrete, brick or block.

Deck Screw

Deck Screws

Deck screws feature a type 17 notched point for removing chips of wood to make it easy to install in wood and composite deck materials.

Lag Screw

Lag Screws

Lag screws, commonly called lag bolts, are large wood screws with threading that extends all the way up the shaft.

Self Drilling Screws

Self-Drilling Screws

Self-drilling screws are screws with a self-drilling (TEK) point to pierce through 20 to 14-gauge metals. The higher the TEK number, the larger the drill point to pierce heavier gauge metals.

Sheet Metal Screws

Sheet metal screws have sharp cutting threads that cut into sheet metal, plastic or wood. They have a fully threaded shank and sometimes have a notched point at the tip to aid in chip removal during thread cutting.

Wood Screws

Wood screws are partially threaded with large cutting threads and a smooth shank. They are designed to slide through the top piece of wood and tightly pull all boards together. A Deck Screw is a variety of a wood screw.

Screw Drive Styles

There are many screw drive styles available depending on the type of screw being installed. The four most popular styles for screws are the following:

	SLOTTED A straight line cut into the center of the head.
	PHILLIPS The most common drive style. Shaped like a cross.
	SQUARE A square shape, resists stripping out.
	TORX / STAR / 6 LOBE Torx drive, also known as star drive, is considered the least likely to strip during a proper installation and provides a more decorative drive finish.

There are many other head types including internal hex (Allen Driven) and other more specialty heads called security heads which include spanner, Torx with pin, Philips with pin, and many more.

Screw Heads

Screw heads serve different purposes, a flat head is used to countersink the screw so nothing remains exposed. While others have more decorative or functional properties. There are many common heads on screws and each usually serves a different purpose depending on the application. Listed below are the common head types found on screws and their functions.

	Bugle Head A Bugle Head is similar to a flat head with a rounded section that will pull down drywall instead of cutting through it as it is fastened.
	Button Head A button head is a rounded head, used primarily in socket cap screws. This head sits above the installation surface.
	Button Flange The button flange head is similar to the regular button head style but with a flange or integrated washer to increase surface area during an installation.
	Fillister Head A head with a higher profile than other head styles.
	External Hex Head This head is designed to be driven by a wrench and allows for high torque installations. The head of all lag screws.
	Hex Washer Head A head that is designed to be driven by a wrench with an integrated washer or flange to increase the installation surface area. A common head for driving concrete screws due to its stronger installation points.
	No Head Exclusive to the socket set screw, lacks a head and has an internal drive in the body of the screw itself.
	Flat Head A flat head is designed to be drilled into a material until it sits flush with the installation surface.
	Oval Head Similar underside to that of a flat head screw but with a decorative rounded top. Commonly used as a finish screw in visible applications.
	Pan Head A screw with a rounded head (less so than a button or round head) and a flat bottom designed to sit directly on the installation surface.
	Pancake Head A flat topped head with a wide head to sit close to flush but also have a large surface area on the installation material for grip.
	Round Head A completely rounded head that was very popular but has become less so with the variety of heads now available.
	Truss Head With a wider installation surface area, this style is used where a lower profile is desired but a strong grip is needed.
	Modified Truss Head Similar to the truss head but with an integrated washer which increases the surface area of the head even more.

Screw Threading

Screws have both coarse and fine threading options available. Both have a place when it comes to choosing screws. Coarse thread screws tend to have a larger pitch and size relative to the diameter. This thicker threading provides more retention and gripping power (resistance to pull-out). Fine thread screws have thinner more frequent threading which prevents these screws from vibrating loose accidentally. Fine thread screws are also considered to be significantly more delicate than coarse threaded screws.

Downside Of Screws

Screws are an excellent fastener to use for a wide variety of projects but have a couple of downsides.

Shear Strength – Screws have a relatively weak shear strength. If the application will be under shear forces, bolts or nails should be used instead.
Hold – Sometimes screws loosen and it can be caused by a variety of factors.
1. Temperature Change which causes the material to expand and contract resulting in a less firm hold.
2. Vibrations cause loosening in most fasteners over-time by rotating them out of their installation.
3. Varying Weight fluctuations in load can cause screws to loosen as well by warping the material and screws themselves.

Helpful Resources

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Screws vs Nails – What’s the Difference?

Screws vs Nails

It’s one of the more common questions asked in our industry. Which applications should use screws and which should use nails? While there is no easy answer as we will soon learn, The basic theory is simple. Screws for holding power and nails for shear strength. But just what does that mean? How do we know when that kind of force will be present? To answer these questions, we sat down with our fastener expert to discuss screws vs nails.

The Basic Theory

Screws

Screws are fasteners with a drive located in the head and threading that protrudes down the length of the shank. Screws (most of the time) require a pre-drilled hole and can often cut their own threads into materials they are rated for. For the sake of argument, we are going to be discussing a deck screw for this example. Deck screws are exceptionally engineered to hold two boards of wood together tightly and efficiently.

Nails

Nails are fasteners with a flat head, smooth shank and sharp point. Nails are driven by a hammer into materials to hold them together. They can be installed faster and are cheaper than screws. In this case (and to explain the theory), we will be using a smooth shank screw as our example.

Comparison

So when comparing nails vs screws we need to consider a few factors. Grip strength and shear strength being the two most important. To view these forces we’ve created some simple diagram. Assume that the arrows are the forces acting upon the two boards in the pictures shown.

Grip strength, in this instance, will refer to a fasteners ability to hold in wood. When a screw is driven its threads dig into the material around it. This makes screws more difficult to remove as they need to be spun out of the wood. So as an example, lets take a tray with a wood board screwed onto the bottom. This board is going to be able to hold quite a bit of weight without the screws falling out. Conversely, if nails were used they would not be able to hold the same amount of weight without starting to loosen.

Shear Pressure — Force being applied on the sides of the two boards.

Now lets look at shear strength. Shear strength is the amount of force a fastener can handle from the sides. A nail, has more elasticity than a screw. This means as forces are pushed against the sides of a nail, the nail can bend slightly to accommodate these pressures. A screw conversely has very little shear strength. Screws that are bent will almost always snap when trying to be straightened.

So which is better a screw or a nail?

The answer is: It Depends. In many applications where force is placed vertically along the installation, a screw is a better choice, but in situations where the force is placed adjacent to the installation a nail is a better choice.

Now a real life scenario where we see this happen all the time is in decking. The forces wind creates on the bottom of a deck (especially in hurricanes) can be catastrophic. As a result, when you install hurricane ties, you want to use nails to install them as the forces that act upon them will shear screws straight off. But these same forces that come up from underneath a deck will push on the bottom of the boards you walk across and since that pressure is pushing directly against the fasteners head, you will want better grip strength making screws the appropriate choice.

As with all fasteners, each has its own unique positive and negatives and must be chosen accordingly. There are also outliers to this rule. Ring shank nails are one of the many varieties of nail available that can provide better retention add some very strong adhesive to that and it’s even less likely to come out. In theory though, the answer is simple. Need grip strength? Use a screw. Need shear strength? Use a nail.

Correct pressure to use a screw for The correct pressure to use a nail for

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What is Torque Control?

Torque Control and Related Terms

Torque is the force applied to something to make it spin (rotate) in machinery. Torque in relation to fasteners is the resistance faced when installing a fastener. Torque control then is simply controlling the amount of torque placed on a fastener without damaging it by over-tightening.

Prevailing Torque	Measure of a screw or nuts frictional resistance to rotation.
Prevailing “Off” Torque	Highest back-off torque on a torque wrench on the first rotation of a screw or nut upon removal.
Installation Torque	The initial torque amount used to install a fastener before Pre-load.
Breakaway Torque	The minimum torque required to start rotation into a nut (in the case of a bolt) or into a pre-tapped hole (in case of a screw).
Breakloose Torque	Minimal torque required to begin the disassembly of a fastener assembly.
Seating Torque	The torque required to produce pressure onto the installation material causing compression by the fastener.

Torque Wrenches are one of the easiest ways to ensure proper torque is met. Simply set the wrench’s torque and then when the maximum is reached the clutch will slip. This slip means the wrench stops putting any more torque on the fastener and it has reached its optimal torque.

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Installing Break Away Shear Nuts

Security Nuts That Shear Under Torque

Break away shear nuts are security nuts that break or shear under a certain pressure. These nuts are designed to be installed and never removed. You will often see them on street signs or in other places where vandalism may occur. These nuts are designed to have a structural flaw in them to create a breaking point.

Installation

The first step in installing these nuts is to hand tighten them onto a bolt. Once you get them snug against the installation material you will need to start tightening them with a shear nuts wrench. Hold the bolt in place with a wrench and then grip the nut end from the other side with another wrench. Spin the wrench onto the nut side and as the nut tightens against the material (use a washer if the material is soft to avoid damage) it will begin to place force on the flaw.

Once the flawed area of the nut reaches its breaking point, half of the nut, the side with the hexagonal gripping area will break off, leaving only a coned end behind.

The end result is a secure fastener assembly that will be incredibly difficult to remove. The cone shape makes gripping devices such as vice-grips effectively useless at removal. The hexagonal end is considered a throw-away part and cannot be reused. Shear nuts are similar to tri-groove nuts in shape, however they do not have the grooves built in that are needed for removal.

shear nut after install

Please Remember that these nuts are very difficult to remove. Make sure you only use them where you never intend on removing them again.

installed shear nut

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How to Install and Remove a Carriage Bolt

Carriage Bolt Install and Removal

The Setup

The first thing we need to do when installing a carriage bolt is to make sure we have the right parts and tools to do so. For this job we will need a:

Hammer
Drill
Drill Bit
Piece of wood
Carriage Bolt
Nut
Washer

For our example, we have already pre-drilled the hole into a piece of 2×4 and attached it to a vice. This will act as our installation surface for our carriage bolt.

Understanding A Carriage Bolt

A carriage bolt is a bolt with threading all the way up the shank to a small square shoulder, with a domed head. The square shoulder of a carriage bolt stops it from spinning as it is screwed into the surface of a material. You would not typically use this type of bolt on very hard wood as it may not properly dig into the material, which would cause the bolt to spin in place. Once you seat the bolt through the hole, it is the job of the nut and washer to pull the bolt into the material tightly. Since there is no drive device for the domed head of the bolt, this is the only way to install it.

The Install

The installation process is fairly simple. First, you drill a hole into the wood for the appropriate size (diameter) of the bolt. Next you slide the bolt into the hole (you may need a hammer as the hole should be just big enough for the bolt to go through).

Now that you have the nut through the wood it is time to attach the nut and the washer. Place the washer on the rear side of the bolt followed by the nut. The washer will help to distribute the force you are about to put onto the nut to pull the bolt into the wood. This will not only protect the wood on the back side but also keep the bolt from digging into it and getting stuck.

As you tighten the nut, the square shoulder on the bolt will be pulled into the wood. Once the underside of the head rests against the wood, the carriage bolt is officially installed.

The Removal

Removing the carriage bolt is a fairly simple process. First, you will want to twist the nut close to the end of the bolt. DO NOT TAKE THE NUT ALL THE WAY OFF THE BOLT, you will need it to help move the bolt along.

Once the nut is backed off to the end of the bolt, hit the nut with a hammer. The force should start moving the square shoulder out of the wood. As you move the bolt further out the nut will get closer to the wood. When this happens continue to back out the nut and strike it again. Repeat this process until the bolt is loose enough to take out by hand or the nut can no longer grip the bolt.

If you find the bolt is stuck but the nut can no longer attach to the bolt, use the nail remover attached to the hammer and use it to pry the bolt out of the hole.

It’s That Simple

There you go now you know everything you’ll need to know about installing and removing carriage bolts. As always, Albany County Fasteners stresses the need for protective gear while working with dangerous materials. Remember to ALWAYS wear safety glasses while drilling to protect your eyes and wear protective gloves that fit to keep your hands safe from harm as well.

Full Installation and Removal process you can find on our Youtube channel

Types of Screws

Screw Terminology

Measuring Screws

Screw Installation

Types of Screws

Screw Drive Styles

SLOTTED

PHILLIPS

SQUARE

TORX / STAR / 6 LOBE

Screw Heads

Bugle Head

Button Head

Button Flange

Fillister Head

External Hex Head

Hex Washer Head

No Head

Flat Head

Oval Head

Pan Head

Pancake Head

Round Head

Truss Head

Modified Truss Head

Screw Threading

Downside Of Screws

Helpful Resources

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Screws vs Nails

The Basic Theory

Screws

Nails

Comparison

So which is better a screw or a nail?

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Torque Control and Related Terms

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Security Nuts That Shear Under Torque

Installation

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Carriage Bolt Install and Removal

The Setup

Understanding A Carriage Bolt

The Install

The Removal

It’s That Simple

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