All types of bolts function as mechanical fasteners that feature external threads and get used in conjunction with a nut to join parts using tightening torque. The fasteners work by getting inserted through holes that are pre-drilled in the material you want to join together, like two pieces of your deck or porch. Unlike screws that also work using externally threaded fasteners, bolts and nuts work together. So, the bolts require a nut to get threaded on it to work properly, and they need a drilled hole to insert the bolt into.
The terms types of bolting or bolting are rarely used when it comes to bolts you use for fasteners. Instead, it’s popular with bolting machines or fabric bolting in the fabric industry. You don’t want to confuse the two. However, if you’re curious as to which types of bolts are available, we’re going to highlight 27 popular types for you below.
Picking out the correct bolt type can be very overwhelming if you’re not sure what is available, so this short list will outline the most popular types available on the current market. IMG_0032 by Robert / CC BY-SA 2.0
27 Types of Bolts
There are several different types of bolts, and they come in different sizes and shapes. It’s even more confusing trying to narrow down the types of bolts when you see that some categories can overlap. Some bolts give you more strength when you pair them with specific materials, while another type of bolt that is normally strong can be weaker when you use it with the same material. You also have to find the right bolt size for your needs. We’re going to try and clear up some confusion below.
1. Aircraft Bolts
This type of bolt is a slightly broad category that encompasses several types of fasteners that have a 12-sided head and give you more strength than you’d get with standard bolts. The head design gives you a much better grip during the assembly process because it offers so much extra area. In turn, you get higher torque levels when you tighten it. Even though there is a broad range of different types of aircraft bolts, it can also include any bolts that meet the standards the DoD sets.
2. Anchor Bolts
These bolts allow you to attach things to concrete, and the bolt head usually gets put right into the concrete before it cures while leaving the threading exposed and ready to use. There are several types of bolts in this category too, but the strongest and simplest is the cast-in-place model. With this bolt, the embedded end comes outfitted with a regular hexagonal washer or bolt, 90-bed, or flange, and the load-transfer mechanism is the mechanical interlock. There are also post-installed anchors, and you can put them into your concrete after drilling.
3. Arbor Bolts
This type of bolt comes with a washer attached permanently, and it has reversed threading on it. They come designed to be used in certain tools, like a miter saw, to ensure that the tool stays secure and the blade stays in the correct place.
4. Bent Bolts
Just like the name suggests, this type of bolt isn’t straight. The end gets shaped or bent to meet specific requirements, like a right-angle bend or an eye-shape. You can find these bolts used in a range of industries, including steel fabrication, waterworks, metal building, and other specialized niches. The most popular types of bent bolts include:
- Anchor Bolts – These bolts typically get attached to concrete to anchor structures in a range of projects.
- Eye Bolts – Typically used to attach the eye to a structure so you have a solid foundation to tie cables or ropes too.
- Offset Eye Bolts (Tie Bolts) – You can use these types of bolts in conjunction with all-thread or tie rods, and you use them to tighten up a connection.
- U-Bolts – When you use this around bent bolts, it works well to attach a steel round bar or pipe to a steel or wood post. You’ll typically see these bolts used with all-thread or tie rods to help tighten up a connection. In mechanical installations, they’re popular to help hang wrought iron pipe. You can embed them in concrete and use them as anchor bolts too.
5. Blind Bolts
This type of bolt usually refers to a style that allows you to use a fastener in instances where you don’t have access to both sides of the bolt to torque or tighten the bolt. A very simple example of this instance is when you use a toggle bolt to secure items to your wall between dual supporting beams. In this case, the portion of the bolt that is behind the drywall’s surface isn’t accessible. So, your entire installation process with the toggle bolt has to be done on the visible or external side of your drywall.
6. Carriage Bolts
Carriage bolts come with a rounded, smooth head with a square section that keeps the bolt from turning, and they offer a threaded section for a nut. You may hear this type of bolt referred to as square neck or round head bolts. There are also usually strengthening plats on either side of the wooden beams, and the beams get fastened using this type of bolt. You’ll also find them used on hinges and locks.
They come made to be aesthetically-pleasing, and the rounded head gives you a very uniform appearance. The bolt’s body is threaded like most bolts are, but when you reach the shank, there are flats or ribs that will keep the bolt in place once you tighten it up. Some of these bolts get pressed into place and others have a pre-punched square hold.
Carriage bolts are a very aesthetically-pleasing bolt type that gives you a very uniform look and feel when you use them due to the rounded, smooth head. Carriage Bolt with Hex Nut by Wil C. Fry / CC BY-NC-ND 2.0
7. Countersunk Bolts
Also known as stove bolts when they work alongside machine screws, this type of bolt gets used in flush-mount assemblies. You can find them in a decent range of sizes and shapes, depending on your need. You’ll find these bolts used in walkways, bridge decking, and railings.
8. Double End Bolts
You may hear this type of bolt called a stud bolt, and they have a threaded portion on each end of the bolt without the additional head. One end gets designed to be threaded into a holt that you tap with a mated thread. The other end will protrude, and it has threading to support a nut. The look of this type of bolt is very similar to a threaded rod, but it traditionally doesn’t get threaded over the entire stud’s length. It can also get threaded differently on each end. Some bolts use a screw thread on one end instead of bolt threads on both ends.
9. Elevator Bolts
These types of bolts come outfitted with special washers, and they get characterized by their flat heads, square necks, and partial threads. You can countersink the square head to help it resist turning, and this makes it easier to turn the actual bolt. They come in different sizes and shapes, and they have different ways of attaching to the surface. So, it’s extremely important that you know you’re picking out the correct bolt for the project at hand.
These bolts are useful because you can use them on soft surfaces, including softwood, while keeping them safe and sturdy. They were originally created to use on lifts and conveyor belt systems because they have an increased load capacity. You may also find them used in vehicle flooring, like campers and RVs because regular bolts wouldn’t survive the constant flexing and bending motion.
10. Eye Bolts
Eye bolts have either a partially or fully enclosed looped end instead of a traditional bolt head. You can use the loop to lift an object in some instances when you attach it. However, some eye bolts don’t work well for lifting. Instead, you’d use them to route cables, wire, or other elements to help avoid accidental interference. They also offer more capabilities depending on the finish and composition. Some are suitable for blending into the background because they don’t reflect light, and others work well in low-temperature operations.
You can get this type of bolt without or with a shoulder at the loop’s base. Other options include having the loop closed or open, including welded, an external or internal thread, and whether or not it comes with a pointed end on it like a wood screw, or if it’s intended to be used with a nut to help secure it. You can get inch and metric sizes available in several different lengths. Also, there are different sized eye diameters that let you use them for a huge range of projects.
11. Flanged Bolts
Flanged bolts, like several other types of bolts here, come with a larger head that makes it easier to identify it and secure the bolt itself. Under the head, the circular flange works like a washer would. It helps distribute the load, and it can give you up to four times the bearing area of a standard hex screw. You’ll see these bolts used in vehicle frames, especially on trucks. If they’re not serrated, you’d call them frame bolts.
12. Hanger Bolts
This type of bolt doesn’t come with a head on it. Instead, it has a machine threaded body with a wood threaded screw tip. If you want to get technical, this is a type of stud instead of a type of bolt, and you can easily use them to suspend objects from wood or attach objects directly to wood. You’ll get threads at each end, and there are lag threads on one end that screw into the wood while the machine screw threads on the other end hold a nut or go into an already threaded hole. This mounting hardware can support up to 300 pounds without a problem.
13. Hex Bolts
As the name suggests, you’ll get a threaded body with a hexagonal head with this type of bolt. The section under the head may not have threads. This is one of the most common fastener types that you’ll find used in just as many projects as a standard bolt. You’ll choose from three standard lengths or grades, and the shank has different diameters that range from ¼-inch up to 4-inches. When you compare it to a square bolt, you’ll get more strength in the hex-shaped head. It’s also easier to assemble, has easier torque application, and the manufacturer’s identification has more area.
14. J Bolts
This type of bolt comes shaped like the letter J. You use them for tie-downs to help hold equipment or materials down to keep it secure and safe on trailers when you transport them from point A to point B.
15. Lag Bolts
You’ll get a square head with this type of bolt, and it has threaded conical points that you use for masonry or wood projects. You use an expansion anchor to apply and secure them to make them extremely sturdy. They work to connect very heavy materials to heavy lumber pieces, and they’re much bigger than regular sheet metal or wood screws. This screw is only available with a hex head on it, while other types of screws feature a large range of shapes.
16. Machine Bolts and Machine Screws
Machine bolts are popular for fastening two pieces of material together, and they’re very similar to hex bolts. The main difference between the two is that they don’t come with a chamfered point. They’re also not designed to have a washer-bearing surface on the head’s underside. You can get them in both square and hex head options. This is a different fastener product that gets used synonymously with machine bolts, and this confuses a lot of people.
Machine screws are smaller in size than this type of bolt, and they typically come with uniform threading along the fastener’s full length. Unlike sheet metal screws or wood screws that have a tapered or pointed tip design, these ones usually feature a flat tip. You’ll normally use them with pre-tapped holes or drive them into materials where the screw creates its own thread in the material as you tighten it up.
On the other end of the spectrum, machine bolts are designed to tighten using torque and having a nut on the end of the bolt. So, while bolts and nuts are usually paired, nuts don’t typically go with screws that you thread into pre-tapped holes. Both machine screws and machine bolts come with different styles of heads, including a hex head. This is very frequently paired with hex nuts, and a few other head styles include cheese, oval, and flat.
17. Penta-Head Bolts
Penta-head types of bolts are one example of a bolt that is tamper-resistant. You can use them in applications where you want to reduce the chances of a person removing or loosening the bolt with standard tools. The bolt’s head comes in the shape of a pentagon, and standard socket or wrench sets aren’t capable of working on these bolts.
18. Plow Bolts
Plow bolts get characterized by the countersunk, flat head design with a square neck and a unified thread pitch. It’s very similar to the carriage bolt we touched on earlier, but you can tell them apart by the flat or concave head this type of bolt sports. The odd design lets you mount it flush to your material, and this is also a key to help prevent it from rotating. Because of this fact, you’ll typically find this bolt used on bulldozers, road graters, plows, and a range of other construction or heavy-duty equipment.
19. Rock Bolts
During the construction of a tunnel, it’s common to use this type of bolt to stabilize the walls while you work.
20. Round Bolts
This type of bolt has a pleasing appearance to it, and it gives your projects a very finished and smooth look. They’re also similar to carriage bolts, but they don’t have a square neck under the head. Instead, the smooth, round head helps you identify them. You tighten this type of bolt up by torquing the nut that comes with them. They’re very popular for use in wood connections.
21. Sex Bolts or Chicago Bolts
This bolt will have both a female and male part to them with bolt heads and interior threads on each end. You’ll find them used in paper binding.
22. Shoulder Bolts or Stripper Bolts
Shoulder or stripper types of bolts have a threaded bolt section that is a smaller diameter than the bolt’s shoulder. The shoulder is the section of the bolt between the beginning of the threaded section and the head. These bolts are very helpful for working as an axle or shaft, and they can have a rotating part to them, like a bushing or bearing.
23. Socket Head Bolts
This type of bolt has a recessed head that you tighten using a hex socket tool or an Allen wrench. The head style on these bolts can vary from a flat-head countersunk style to a cylindrical profile to a domed button head, depending on the use. The deeper recessed Allen socket head gives you the ability to increase how much torque you apply to the fasteners while reducing the chances of damaging or stripping the head. You may hear this type of bolt called a socket head cap screw.
24. Square Bolt
Also known as square bolts, this type of bolt was once very commonly used before hex head bolts came about. You can still find these bolts, but they’re mostly used in railway applications to give you the correct design aesthetic of a more traditional and older appearance. You can get these bolts in high, medium, or low strength grades and they have both a T-slot or square head option. Stainless steel and steel are the most common material, and you can get partially or fully threaded designs. Some suppliers call these screws instead of bolts.
The square heads on this type of bolt can sometimes have a decorative look to it to help mimic older styles. They can be hammered, pyramid-shaped, or have an irregular appearance to them that reflects the way these fasteners were originally made using a hand-forging technique before mass production came about.
25. T-Head Bolts
T-slot or T-head bolts have a head design that lets you insert it easily into a recess or slot, and this will secure the bolt in place to stop it from turning when you tighten up the securing nut. You’ll see this type of bolt used to secure fuel tanks in place where you may not have access to both sides of the bolt at all times. The T-slot variety can be fed into a machine’s channel called a T-slot track, and you use it to secure an object in any position that you like along the channel’s length.
26. Track Bolts
As the name suggests, these types of bolts were originally popular for use on the railroad tracks. You may hear them called anchor bolts or fang bolts, and you use them to fasten link rails to rail joints or rail chairs and steel rails to railroad ties. They’re very high-quality and strong bolts that resist vibrations. They come in a range of shapes and sizes that include but are not limited to:
- Anchor bolt
- Button head oval neck track bolts
- Clamp bolt and inserted bolt for Russia
- Clip bolt HS26 & HS32
- Clip bolt with a BSW thread
- Diamond neck track bolts
- Fish bolt used for rail joints
- Rail bolt NF F50-008
- Special bolt
- Tunnel bolt
Because of the strict safety requirements, you’ll have special requirements for these types of bolts. They have to be the correct size and shape, and you have to have them tightly in place at all times. You have to install them with AREMA spring washers, and you have to lubricate and clean the areas correctly. If the bolts are ineffective or missing, there are rules in place to ensure that it gets fixed.
The final type of bolt on the list is a U-bolt, and they come in the shape of a U. There are two male threads with one being on each end. You add a mounting plate bracket and attachment nuts on the ends. Most U-bolts come with a semi-circular profile to them, but some have a squared-off shape. They’re usually not fully threaded, and they work to clamp an object in place.
You can find this bolt used in a range of applications from the automotive industry for use on exhaust systems and drive shafts to supporting pipes. Some designs have a rubberized coating to help ward off wear due the metal-on-metal movement, and some come with thicker rubber gaskets to reduce vibrations and lower the noise levels. You can get non-metallic designs for projects where there is a risk of the U-bolt coming into contact with an electrically powered conductor.
Five Popular Materials for Types of Bolts
The bolt material you get will depend on what you want to use the bolt for, and there is a special emphasis on what materials you want to fasten with it. There are levels that make the bolt stronger amongst different materials. For example, a Grade 2 bolt features hardware-grade steel.
Grade 5 alloy steel is a medium zinc-carbon plated alloy steel that goes through a heat treatment to increase how hard it is. Grade 8 steel gets hardened to another level to allow you to use it in very demanding circumstances, like in automotive suspensions. The five most popular materials for bolts are:
Picking out the material for your bolt will have a big impact on how it performs in the long run, especially if you live in more wet environments. Industrial Chess by Matthew Matheson / CC BY-NC-ND 2.0
Bronze is an alloy that has copper. It can also routinely contain non-metals and metals. You can use bronze when you need to have a waterproof product. This is why you see bronze bolts used in marine environments, especially in the repair or construction of wooden boats.
Nylon is a much lighter material for bolts, but this is exactly why it’s such a popular material choice when you need a lightweight and waterproof material. Since it’s not as strong, the bolts can’t support as much weight as most other types of bolts. However, they’re very useful for holding materials like rubber, plastic, matal, and particleboard. You’ll find them used in home appliances like washing machines.
This is a steel alloy that gives you extra protection and strength. As an alloy, this material has a natural resistance to corrosion. This makes it very useful for certain construction projects where you’ll have your bolts exposed to the elements. It also won’t lose any special properties, even if it gets damaged or scratched. This is why stainless steel bolts are very popular to use in areas with high levels of pollution or in areas close to the water.
This is one of the most common materials to make different types of bolts out of. It’ll also work for most purposes, and 90% of bolts use normal steel for the main material. Due to the low price and the high strength point, you can use it in almost any job where you have environmental problems.
Finally, titanium resists corrosion, is lightweight, and is very strong. Any types of bolts that feature this material get used where you need a high strength to weight ratio, and it’s up to four times stronger than stainless steel. You may see these bolts used in ships, airplanes, and submarines.
We’ve outlined 27 popular types of bolts for you, and you can take this list and see which ones will suit your upcoming projects the best. Getting the correct bolts will help ensure that your project goes smoothly from start to finish, and it also gives you the reassurance that they can last for years without failing.