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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

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

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 drive

SLOTTED

A straight line cut into the center of the head.

phillips drive

PHILLIPS

The most common drive style. Shaped like a cross.

square drive

SQUARE

A square shape, resists stripping out.

torx

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

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

Button Head

A button head is a rounded head, used primarily in socket cap screws. This head sits above the installation surface.

Button Flange

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

Fillister Head

A head with a higher profile than other head styles.

External Hex Head

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

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

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

Flat Head

A flat head is designed to be drilled into a material until it sits flush with the installation surface.

Oval Head

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

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

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

Round Head

A completely rounded head that was very popular but has become less so with the variety of heads now available.

Truss Head

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

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
  1. Why Do Wood Screws Have A Shank?
  2. Fastener Measuring
  3. Fastener Varieties
  4. Fastener Drives, Heads and Threads

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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

Grip Strength
Force being applied to the top or bottom of the two boards.

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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