Screw: Definition, Types, and Types of Screw Head

What is screw?

A screw is a broad category of mechanical fastener with a threaded shaft, designed to screw into a part. This includes wood screws and self-topping screws, which have a tapered shaft with sharp threads designed to cut a mating thread in the part to which they are fastened.

These grooves can be either throughout the shank or only in the beginning. These grooves provide necessary friction and traction to avoid pull-out.

Also known as a male (or external) thread. Typically made of metal, screws fasten materials by digging in and wedging into them by turning, upon torque applied. A screw is sometimes also known as a cap screw or tap bolt.

Note: Those who don’t know ‘What is a fastener?’. A fastener is a hardware device that mechanically affixes or joins two or more parts together.

On the basis of the threading mechanism, there are basically two types of screws.

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1. Self-threading screws

When we move self-threading screws clockwise (with some pressure) against the joining material, it makes its way into the material (mainly because of its sharp tip). They are generally suitable when the joining parts make by either wood or plastic.

In many cases, self-threading screws can also insert into joining parts with the help of a hammer, for example in the case of wood and plastic.

2. Non-self-threading screws

In the case of non-self-threading screws, we have to first make suitable helical grooves in the joining material and then insert the screw carefully. They commonly use when the joining parts are build of metal.

Parts of Screw

part of Screw
parts of screws

Parts of screws can mainly be divide into five parts.

  1. Head: It is the topmost part of a screw. A screw can be tightening or loosen from the head of the screw. It has provisions for accommodating a screwdriver or wrench.
  2. Not threaded shank: This is the part of the shank which do not have threads. This part could be absent in some screws.
  3. Threaded shank: This is the part of a screw having threads on it. It is the place from where the screw gets its grip on joining bodies. It has helical grooves in it.
  4. Screw Drive Head: A special design is cut into the head of the screw that the screwdriver will fit into when the screw is driven into a surface. This is called a drive. There are many different designs of drives, but the three most common are Schlitz, Philips, and Pozidriv.
  5. Tip: It is the bottom-most part of the screw. Tip helps screw-in penetrating through the joining bodies. It could be missing in some screws where threads are already present in joining bodies. It is an essential part of self-threading screws, as mentioned earlier.

What are screws made of?

The following material can use in the manufacturing of screws:

  • Titanium: Screws made of Titanium are hard, strong, light, and corrosion-resistant. When alloyed with other materials it can increase strength and durability.
  • Stainless steel: Screws made from stainless steel are chemical and corrosion-resistant. They have an appealing surface finish. They cannot harden like carbon steel.
  • Hardened steel: Screws made from hardened steel are hard but brittle in nature.
  • Steel: Screws make from steel are strong but they are vulnerable to corrosion.
  • Plastic: Screws made from plastic are inexpensive and corrosion-resistant. They use for light loads. They commonly use near water, such as water pools.
  • Molybdenum: Screws made from Molybdenum have a very high melting point and are exceptionally strong.
  • Copper alloy: Screws make from copper alloy have good load capacity and are wear-resistant. They are suitable for use near magnets.
  • Brass: Screws made of Brass are strong, conductive, and corrosion-resistant. They have low magnetic permeability.
  • Aluminum: Screws make of Aluminum are light and easy to manufacture. They are thermally and electrically conductive. They are resistant to corrosion.
  • Superalloys: Screws made of superalloys show good mechanical strength, surface stability, corrosion resistance, and resistance to creep at higher temperatures.
  • Apart from the above material, sometimes some finishing material used in screws. It can provide durability and corrosion resistance to the screw. Here are some finishing materials used in screws.
  • Zinc: Its coating acts as a sacrificial anode, protecting the underlying metal. It is applied as fine white dust.
  • Chrome: Its coating gives a bright, reflective finish. It is decorative and very durable. It is applied by electroplating.
  • Black oxide: Its coating is mostly used for aesthetic purposes. It does not enlarge the dimensions of the screw. It processes black rust.

Types of screws

1. Wood screw

Wood screws are commonly made of bronze, brass, or steel and are used specifically while working with wood.

Their unthreaded shanks at the top and coarse threads at the pointed end make them easy to identify.

The design also serves as more than just an ID—it allows the screw to smoothly penetrate through wood fibers without causing too much splintering (splintering is reduced by minimizing resistance).

Wood screws can have flat, oval, or round heads. Flatheads are important fasteners for instance when you need screws hidden or sitting flush on the wood surface.

Oval heads or pan heads are slightly more visible than flatheads, whereas round heads are the most visible and are, therefore, used for decorative purposes. I used all kinds of random wood screws I had saved in a drawer with my makeshift pallet Adirondack chair.

2. Drywall screws

Drywall screws are meant for drywall panels and come in two basic types—coarsely-threaded or W-type screws used to attach drywall to wood, or finely-threaded or S-type screws used to attach metal studs to the drywall.

The latter also comes with a self-drilling tip, so you don’t need to pre-drill. Drywall screws cut through drywalls like a hot knife through butter, thanks to super-sharp tips that reduce tearing while going in fast.

Many different types of drywall screws exist, including those coated with zinc, phosphate, or ceramic and some that are meant to reduce corrosion. They work well with drywall alternatives, too.

3. Self-Tapping Screws

Self-tapping screws are screws that eliminate the need to pre-drill, thanks to threads that facilitate the drilling of the hole while the screw is being inserted. These screws can be drywall, wood, or sheet metal screws.

However, the problem with these screws is that pulling them out results in stripping the screw. They also easily snap when over-tightened.

4. Sheet Metal Screws

Sheet metal screws can be used in any scenario that requires different materials to be put together, whether it’s rubber, plastic, metal, or any types of plywood.

Therefore, sheet metal screws are available in many types and sizes and the material you’re working with will dictate which screw you use.

Types A, B, and AB are the most commonly found and used sheet metal screws, while Type 25 is rarer and used for specific purposes, generally with plastic. They also come with different heads—hex washer, flat and oval.

Sheet metal screws are extremely efficient thanks to their sharp, customized threads that ensure a tight bond.

5. Masonry Screws

Also called ‘anchors’, masonry screws can be easily told apart from the rest of their family by the lack of a pointed end. Therefore, masonry screws aren’t meant for boring holes and ergo, pre-drilling is required (though a normal drill works, a hammer drill is recommended).

These screws are used to attach concrete to wood or metal, with one of their most common uses being attaching wooden floor plates to the basement floor or concrete foundation.

Masonry screws can have Philips’ heads or raised hex heads that require specific hex-head bits that match (the packaging will tell you which bit and size are required).

6. MDF Screws

A common appearance in homes in molding, crown molding alternatives, and the construction of shelves and bookcases (especially those that require assembly), medium density fiberboard screws are among the most commonly used screws.

These screws are extremely tough screws, since MDF, as a material, is harder than solid wood and quite difficult to pierce. Using wood screws on MDF will, more often than not, result in splitting, unless you pre-drill a hole and then use a normal wood screw.

MDF screws make life easier, especially if you use self-tapping ones. By nature, MDF screws eliminate the need to predrill and the occurrence of splitting. They feature star-drive heads and are available in the same sizes that regular wood screws come in.

7. Decking Screws

Decking screws are most commonly used to install or fasten exterior decking or deck flooring to a joist system. Therefore, these screws are designed to countersink, meaning that they sit flush or are very slightly below the wooden surface.

Decking screws are similar to wood screws, in that they feature coarse threads and a smooth top shank. They are also designed to resist corrosion and rust—another similarity they share with wood screws.

In case you’re using pressure-treated wood decking, only ACQ-compatible decking screws should be used. In case it’s composite decking, most manufacturers specify the use of stainless-steel decking straws for installation.

Decking screws come in various lengths, depending on their purpose and many are self-tapping.

8. Dowel Screws

Also called double-ended screws (for obvious reasons) and wood-screw threaded studs, dowel screws don’t feature heads; instead, they feature lag threads on both ends that taper to a blunt midpoint.

These screws are designed for insertion into pre-drilled pilot holes, but their threads also let them be drilled into the wood without any pre-drilling.

Dowel screws are commonly used to fasten or join two pieces of wood. This makes them a common feature in furniture making, finial installation, creating end-to-end joints and other woodwork applications, especially those involving blind holes and single hidden fasteners.

The lack of a head means that a driver tool or locking plier is required for installation.

9. Mirror Screws

These are specialized screws that help you fasten mirrors to walls sans any additional brackets. Mirror screws feature a slotted countersunk head with a threaded hole; this enables the included cover caps to be screwed on, resulting in easy installation and a stylish finish.

Mirror screws also feature tapered rubber grommets. These prevent the screws from pressing into the mirror directly.

The screws and covers are all coated with zinc, keeping them resistant to rust. This means that these screws can also be used in moist settings, such as bathrooms, without any problem.

10. Chipboard Screws

Also known as twin fast screws and particle board screws, chipboard screws, as the name suggests, are self-tapping screws that are meant particularly for chipboard.

The coarse thread, with two times more thread pitch than standard wood screws, makes it easy to drive them into chipboard, particleboard and fiberboard of different densities.

Due to their ample thread, they can also be easily inserted using ordinary drive bits and hand screwdrivers. The self-centering point on the screw also helps it go in straight and reduce the risk of splitting in the chipboard.

11. Security Screws

Also known as tamper-proof screws, security screws are more or less standard screws; however, they feature unique heads, which means that common tools cannot possibly remove these screws.

Therefore, any screw that you can’t remove with a Phillips head driver or a slot-style head driver automatically became a security screw.

However, humanity has always found a way around things, which means that security screws are not really so secure anymore, thanks to the innovative minds of those who’ve invented driver bits to get through any screw.

Though the problem may not lie in the security screws themselves, the abundant number of driver bits is definitely a problem.

12. Hammer-Drive Screws

Designed for heavy-duty fastening, hammer-drive screws are also known as U-drive screws, non-slotted round head screws, or simply drive screws. Their rounded heads and unique build ensure that they’re strong, durable and last you in the long run.

Hammer-drive screws are most commonly used to attach signs on the wall, nameplates, or other similar purposes. They also feature multiple start threads and large helical angles, along with a pilot point that’s unthreaded.

You can use hammers, mallets, or hammer-drive devices to quickly and permanently drive these screws in. You may require an undersized pre-drilled pilot and the screw must be made of a material that’s harder than the part you intend to drive it into.

Types of Screw Heads

There are a variety of types of screw heads for different materials, and for different applications; screws are often used to fasten sheet metal, wood, and plastic.

Types of Screw Heads
Types of Screw Heads
  1. Binding/Binding Undercut: The ‘binding’ type is a commonly use screw head type. It is an ideal choice for electrical applications; beneath the head is a prominent undercut area providing space for wire connections. Binding screws are also used for other kinds of projects; they are often using to hold together large manuals, for bookbinding, and in leather products.
  2. Trim: The ‘trim’ screw head is a standard countersunk screw that provides a flat, smooth surface after installation. It is an alternative to flat head screws, with a narrower head a more suitable choice for certain applications. The Flat Trim is often used as a finishing screw for carpentry and woodworking.
  3. Oval Undercut: The ‘oval undercut’ is ideal for shorter screw lengths which require longer thread grip and more shallow countersinking.
  4. Fillister: A smaller diameter, in addition to a higher profile, than round or pan heads, makes the ‘fillister’ screw head effective for a deeper slot.
  5. Flat Fillister: The ‘flat fillister’ is identical to a regular fillister screw, except for a flat top replacing the latter’s oval top.
  6. Flat 82+: The Flat 82+ head is use for flush surfaces. They are standard countersunk flat head screws.
  7. Flat 82+ Undercut: The ‘flat undercut’ is very similar to the standard 82-degree head, having the same angle, but a shorter head. This allows it to provide a longer thread on the same screw length.
  8. Flat 100+: The Flat 100+ uses a 100-degree angle instead of the standard 82-degree kind. It is an ideal choice for thinner materials that require a flatter head.
  9. Flat 100+ Undercut: The Flat Undercut is use instead of the standard flat head for some short sizes. The 100-degree kind enables more shallow countersinking than standard 82-degree flat heads.
  10. Hex: Hex heads allow greater torque to be applied, and are driven with the force working against the outside of the head, unlike other varieties, which are internally driven, They are commonly used for bolts.
  11. Pan: The ‘pan’ head is the most commonly used rounded-top screw head. It works well in a range of applications that require a flat-bottomed screw.
  12. Hex Washer: The ‘hex washer’ head is an updated, more commonly used version of the hex head. It is characterized by an attached washer style flange under the head, creating a large surface connection area. It is sometimes used in combination drives, with Philips or slotted drives.
  13. Oval: It is identical to a flat head, except for its rounded surface. Countersunk screw head that includes a decorative rounded finish at the top. Often used for switch coverings.
  14. Oval trim: The ‘oval trim’ head is the same as the regular ‘oval’ head, but with a smaller diameter and countersink.
  15. Round: The ‘round’ head is less commonly used these days, but it offers a round-surfaced alternative to other screw heads.
  16. Round Countersunk: It is similar to ‘flat’ heads, but with no driving recess. The ‘round countersunk’ head use for shorter screw lengths to provide a longer thread grip and more shallow countersinking.
  17. Round Washer: The round washer is a screw head which provides a larger bearing surface in applications where a round head is preferred. It is quite similar to the Modified Truss head style.
  18. Square (Set Screw): The ‘square’ head is a suitable choice for applications that require more torque. It is most often used for switch coverings
  19. Truss: Truss’s heads characterize by a curved surface and an extra-wide top. They regularly use to prevent tampering., having a lower profile than most round heads. Truss heads are very useful for sheet metal work, insulation, and cabinetry– an ideal choice for applications that require large holes, as the wide head prevents the screw from going through the hole.

Types of Screw Head Drivers

Types of Screws Driver

1. Slotted head Drive

The first of its kind to develop, the slotted type is still the most widely available screw drive because it is simple, inexpensive, and effective. The design characterizes by a single line running through the middle of the head, into which a flat-bladed screwdriver fits.

The slotted screw drive works best when hand-driven; it regularly not use with power tools because of the danger of the screwdriver slipping out of the slot and damaging the surrounding material. It is most suitable for simple carpentry, where the torque applied is less.

2. Phillips Head Drive

The Philips screwdriver was introduced to improve the quality of the performance when the head came into contact with the screwdriver. It got its name from the Phillips Screw Company after they bought and modified the design. A Phillips drive characterizes by slightly tapered flanks, a pointed tip, and rounded corners.

In contrast to the slotted drive’s two-point contact, the Phillips head type has four. With a four-point contact, either one of the head types can be used. Like the former, it also burrs when more torque is applied.

3. Pozidriv

The Pozidriv screw is an eight-point contact — a second cross is added to the first, improving the contact of the screwdriver to the head. The Pozidriv is distinguished by a set of radical indentations at 45 degrees, making it visually distinct from the Phillips drive.

The two are broadly interchangeable; but when used incorrectly, either can cause significant damage.

While a Pozidriv may fit a Phillips head, it is not advisable to use the former drive on the latter head, as it may slip out or tear it out. In addition to its superior grip, it is more versatile than the Slotted and Phillips drive.

4. Square Drive

Also known as the Robertson drive, its distinct design characterizes by a square-shaped socket in the screw head and a square protrusion on the tool. The tool and the socket are both slightly tapered.

Originally introduced to make screws more practical through the cold forming of the head, the taper also makes inserting the tool easier, and the screw tends to stay steady on the tip of the tool without needing the user’s support.

The Robertson drive is an extremely popular choice for woodworking and construction, while a combination drive of Robertson and Phillips type is frequently used in device and breaker terminals, as well as in clamp connectors.

5. Six Lobe Drive

Also, refer to as the ‘Torx’ drive style, or a star drive, its design characterize by a six-pointed star shape. The Torx drive is a more recent competitor to the Phillips drive; as is the case with the latter, screw heads of different sizes require different-sized drivers.

Manufacturing process of screws

There are three major steps in manufacturing a screw.

  • Heading
  • Thread rolling
  • Coating

The screw is usually made from the wire. The wire is then cut to the proper length for the type of screw being made. Heading produces the head of the screw. The shape of the die in the machine dictates the features to press into the screw head, for example, a round head screw uses a round die.

The threads usually produce via thread rolling. However, some are a machine. Finally, a coating, such as electroplating with zinc or black oxide, is applied to prevent corrosion.

Uses of Screw

Uses of screw-in following conditions:

  • When the parts that join, are thick enough to accommodate the threaded hole.
  • Bolts are good for frequent dismantling and reassembling, unlike screws.
  • Relative advantages and disadvantages of screws and bolts.
  • When the parts that are attached, that have sufficient strength to accommodate durable threads.
  • These use when the parts sometimes dismantle.
  • There is no place to accommodate the nut.
  • Screws are cheaper compare to bolts.
  • Bolts carry the load on a larger shank area when compared to the screw

Advantages and Disadvantages of screw and bolt

  • Screws are cheaper compare to bolts.
  • Bolts are good for frequent dismantling and reassembling, unlike screws.
  • Bolts carry the load on a larger shank area when compared to the screw.

FAQs.

What Is Screw?

A screw is a broad category of mechanical fastener with a threaded shaft, designed to screw into a part. This includes wood screws and self-topping screws, which have a tapered shaft with sharp threads designed to cut a mating thread in the part to which they are fastened.

What Are The Types Of Screw?

Different Types of Screw:
1. Wood screw
2. Machine screw
3. Lag Screw
4. Sheet metal screws
5. Twin fast Screw
6. Security Screw
7. Concrete screw or masonry screws
8. Drywall screw

What Are The Types Of Screw Threads?

The following are Different Types of screw thread:
1. British Standard Whitworth (B.S.W.)
2. British Association (B.A.) thread
3. American national standard thread
4. Unified standard thread
5. Square thread
6. Acme thread
7. Knuckle thread
8. Buttress thread
9. Metric thread

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