What are Bolts and Nuts?
Bolts and nuts are hardware fasteners commonly used in construction, manufacturing, automotive, and various other industries. They are used to join two or more components together securely.
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Bolts typically consist of a threaded shaft with a head at one end. The head may be hexagonal, square, or another shape, designed for a specific tool like a wrench or a socket. The threaded portion extends from the head to the tip.
On the other hand, nuts are a small metal block with a threaded hole in the center. They are designed to be paired with bolts. When a bolt is inserted through holes in two or more objects, a nut is screwed onto the threaded end of the bolt to hold the objects together.
When we talk about bolts and nuts, there are other hardware fasteners commonly used with them, namely screws and washers.
Washers are thin, flat discs which are used in conjunction with screws, bolts, or nuts to distribute the load of the fastener over a larger surface area and prevent damage to the surface being fastened. Washers also help prevent the loosening of the fastener over time by providing a smooth bearing surface and reducing friction.
Screws are similar to bolts but typically have a pointed tip and are designed to be inserted into a pre-drilled hole. Like bolts, screws have a threaded shaft and a head. Screws are commonly used in woodworking, metalworking, electronics, and many other applications.
How Do Bolts and Nuts Work?
Bolts and nuts are fasteners that work together to hold objects in place. A bolt is inserted through aligned holes in the objects, and a nut is threaded onto the bolt&#;s end. Tightening the nut secures the objects.
Materials of Bolts and Nuts
Bolts and nuts are available in various materials, each with its own characteristics and suitability for different applications. Here are some common materials used for bolts and nuts:
1. Steel
Carbon steel: Affordable and versatile, carbon steel bolts and nuts are widely used in many applications. They offer good strength and moderate corrosion resistance but may rust over time if not protected.
Stainless steel: Known for its excellent corrosion resistance, stainless steel bolts and nuts are suitable for applications where resistance to rust and corrosion is essential. They are often used in outdoor and marine environments.
2. Brass
Brass bolts and nuts are corrosion-resistant and have good electrical conductivity. They are commonly used in electrical and plumbing applications where conductivity and corrosion resistance are important.
3. Aluminum
Aluminum bolts and nuts are lightweight and have good corrosion resistance. They are often used in applications where weight is a concern or where corrosion resistance is required, such as in aerospace and marine industries.
4. Titanium
Titanium bolts and nuts are lightweight, strong, and highly corrosion-resistant. They are commonly used in aerospace, medical, and automotive applications where high strength-to-weight ratio and corrosion resistance are critical.
5. Copper
Copper bolts and nuts are known for their excellent electrical conductivity and corrosion resistance. They are often used in electrical applications and in environments where corrosion resistance is essential.
6. Plastics
Plastic bolts and nuts, such as those made from nylon or polyethylene, are lightweight, corrosion-resistant, and non-conductive. They are commonly used in applications where metal fasteners may cause corrosion or electrical conductivity issues, such as in electronics and plumbing.
When selecting the material for bolts and nuts, consider factors such as strength, corrosion resistance, conductivity, weight, and cost, as well as the specific requirements of your application. Choosing the right material will ensure that the bolts and nuts perform effectively and reliably in their intended environment.
Sizes of Bolts and Nuts
The sizes of bolts and nuts vary based on different standards and measurements. Here are some references to help understand the sizes of bolts and nuts:
Bolt Sizes
- Bolt sizes are often specified using diameter and thread pitch dimensions in millimeters. For example, M8-1.0 x 20 indicates a bolt with an 8mm diameter, 1.0mm thread pitch, and 20mm length.
- Metric bolts can have coarse, fine, or extra fine thread pitches. Coarse threads have more threads per inch compared to fine threads.
Nut Sizes
- Nuts are also commonly referenced using &#;M&#; sizes in millimeters (e.g., M3, M8, M12). The size of a metric nut is specified by diameter and pitch dimensions.
- Hex nuts with diameters under 1/4&#; are called hex machine screw nuts.
- Standard spanner and allen key sizes for commonly used metric nuts include M5, M6, and M8.
Understanding these size specifications is crucial for selecting the right bolts and nuts for various applications based on diameter, thread pitch, length, and other factors.
Thread Types for Bolts and Nuts
Nuts and bolts are threaded either coarsely or finely.
- Coarse-threaded nuts and bolts have more space between the threads, so match the threading of a nut to the threading of a bolt. They will be distinguished by a higher thread pitch. Coarse-threaded bolts and nuts may be fastened faster because they are less likely to get stuck or cross-threaded.&#;
- Fine-threaded nuts and bolts with smaller thread pitches have less thread gaps, resulting in a tight, strong grip. A fine-threaded bolt&#;s nut is less likely to be dislodged by vibrations but installing or removing the nut will take longer.
Types of Bolts and Nuts
Types of Bolts
In the industrial sector, various types of bolts are used to meet specific application requirements. Here are some common types of bolts found in industrial settings:
Bolts with Hex Heads
A hex bolt&#;s hexagonal head serves as a surface for grasping or twisting the bolt with a wrench, socket and ratchet, or drill/driver. Some hex bolts have threads that extend the whole length of the shank and are often used in threaded holes. They provide high grip strength because they distribute tension over the whole bolt. The thicker, unthreaded segment of a partially threaded bolt provides strength to the fastening process. Partially threaded hex bolts are also beneficial for operations that need more force to hold the workpieces together. Hex-head bolts are commonly used in construction and automotive applications.
Carriage Bolts
The domed head of a carriage bolt provides it with a smooth, polished appearance. It also adds a layer of safety and security since it does not have a driving surface like a hex-head bolt. Carriage bolts are fastened with washers and hex nuts after being inserted into pre-drilled holes. The nut is secured to the workpiece by a square area under the head, allowing you to attach it with a single wrench, socket, or driver bit. Carriage bolts are used in a wide range of applications, such as decks, furniture, and outdoor playsets.
Anchor Bolts
Anchor bolts are classified as either those meant for use in concrete foundations or those intended for use in a wall. L-bolts are intended for usage in wet concrete. While the concrete cures, the bolt is kept in place. L-bolts may be used to secure a deck post to a concrete pad. To secure retrofit anchor bolts in existing concrete, an adhesive is employed. When drilling into a wall stud is not possible, toggle bolts provide support for hanging things.
U-Bolts
U-bolts have two threaded shanks with a rounded or flattened appearance. Rounded U-bolts are used to secure pipe or conduit to a surface, while squared U-bolts are used to fasten things to a surface, such as a square post. The U-bolt is held in position against the item being secured by two nuts and a metal plate.
Eye bolts
Eye bolts have a loop or ring end and a threaded end for attaching a chain or rope to a wood, metal, or concrete surface. Eye bolts are designed to be used in pre-drilled holes and come with a matching nut. Screw eyes are similar in appearance but have coarser self-tapping threads and a pointed tip that enables them to be driven into a pilot hole in a woodwork item.
Stud Bolts
Stud bolts are threaded rods with threads on both ends, used to secure flanges together in piping systems or other applications where a nut is required on both ends of the bolt. They are commonly used in oil and gas, petrochemical, and power generation industries.
Lag Bolts
Lag bolts, also known as lag screws, have a coarse thread and a hexagonal head designed for use with a wrench or socket. They are used for securing heavy materials to wood, such as attaching lumber to concrete or wood-to-wood connections.
Tension Control Bolts
Tension control bolts feature a unique design with a spline section beneath the head and a cone-shaped washer. They are installed using a specialized wrench that breaks off the spline after reaching the proper tension, providing a reliable and controlled bolt preload. They are commonly used in structural steel connections.
Flange Bolts
Flange bolts have a washer-like flange under the head that distributes the load and provides a larger bearing surface. They are commonly used in automotive, plumbing, and machines.
Types of Nuts
In the industrial sector, there are various types of nuts used for fastening components together. Here are some common types of nuts:
Hexagon Nuts
Hex nuts have a six-sided driving surface. They are a common sort of nut used to connect wood and metal components with bolts of the same size and thread type.
Lock Nuts
Nylon lock nuts have a hexagonal head with an integrated nylon ring. When you tighten a lock nut onto a bolt, the threading of the bolt displaces or deforms the ring, causing friction and preventing loosening from slippage or vibration. A castle nut is a kind of locking nut that works by putting a pin or clip into a hole in the bolt. Rotation is restricted when notches etched into the nut come to rest on the pin.
Wing Nuts
Wing nuts are designed to be tightened and loosened without the need of tools; the wings allow you to tighten and loosen them with your thumb and finger. These nuts are used to make adjustments and removals quick and easy. They may be found on drum sets, light stands, and other items that need to be adjusted on a regular basis.
Cap Nuts
Cap nuts, sometimes known as acorn nuts, are domed and feature a hexagonal driving surface. They are often hand installable. They screw onto the exposed threads of a bolt or threaded rod to protect them and provide a decorative look. Cap nuts may be found in projects like outdoor playsets and fences.
Square Nuts
Square nuts have four flat sides and are designed to be used with square bolts or in channels or tracks where rotation prevention is required. They are commonly used in construction, machinery, and automotive applications.
These different types of nuts cater to specific performance advantages and application scenarios in various industries, ensuring secure fastening of components based on specific requirements and usage scenarios.
How to Choose the Right Bolts and Nuts
Choosing the right bolts and nuts for your project involves considering several factors, such as the material, size, thread type, strength, and environmental conditions. Here is a step-by-step guide to help you select the appropriate bolts and nuts:
- Identify the Application Requirements: Determine the specific application requirements such as load-bearing capacity, environmental conditions (temperature, moisture, corrosion), and material compatibility (e.g., compatibility with other materials being fastened).
- Select the Material: Choose a material suitable for the intended application. Common materials include steel (carbon steel, stainless steel), brass, aluminum, and titanium. Consider factors such as strength, corrosion resistance, and cost.
- Determine Bolt Size and Length: Measure the thickness of the materials being fastened and select a bolt length that provides enough thread engagement for a secure connection. Choose the appropriate bolt diameter (e.g., M6, 1/4 inch) based on the load requirements and the size of the holes in the components.
- Select the Thread Type: Determine the appropriate thread type for your application. Common thread types include coarse thread, fine thread, metric thread, and specialized thread. Ensure that the bolts and nuts have compatible threads to ensure a proper fit.
- Consider Strength Requirements: Choose bolts and nuts with sufficient strength to withstand the expected loads and stresses. Bolts are typically graded based on their strength. Consider factors such as tensile strength, yield strength, and shear strength when selecting bolts and nuts.
- Evaluate Environmental Factors: Consider the environmental conditions in which the fasteners will be used (e.g., exposure to moisture, chemicals, and high temperatures). Select materials and coatings that provide adequate corrosion resistance for the specific environment.
- Consider Specialty Features: Depending on the application, you may need specialty features such as locking mechanisms, tamper resistance, or high-temperature resistance. Choose bolts and nuts with the necessary features to meet the specific requirements of your project.
By following these steps and considering the relevant factors, you can choose the right bolts and nuts for your project, ensuring a secure and reliable connection.
You&#;d expect an engineer to know everything about a basic subject like nuts and bolts right? Well fasteners are one of those topics that seem simple at first but turn out to have much more depth than you expected. What follows are 10 tricks on this &#;basic&#; subject that might surprise you!
UPDATED MARCH : It has come to my attention that there is testing data available that makes the counter argument to my first point in this article. In the interest of transparency and good scientific discussion, I&#;ve provided links to all sources mentioned at the end of point #1. When faced with contradictory test results, if we assume the methodology and integrity of all sources are without fault, it is reasonable to conclude that your results may vary. Many factors could significantly affect testing results including variances from manufacturing process, fastener & clamped materials, heat treating, surface finishes, ambient conditions, and bolt diameter.
1. Split washers have been experimentally proven to be ineffective locking devices and can even aid self loosening over time. And yet I see these things in use everywhere, so what gives?
In theory split washers (aka lock washers or helical spring washers) are supposed to work by squishing flat between the nut and the mounting surface when you tighten them. At this point the sharp edges of the washer are supposed to dig into the nut and mounting surface to prevent counter-clockwise rotation.
In practice a split washer is unable to gain any purchase against hard surfaces and does not actually prevent rotation. The problem is that split washers make for poor springs and bottom out after only a small percentage (on order of 10%) of a bolt&#;s total clamping load.
The only time a split washer might prove useful would be for fastening onto soft easily deformed surfaces such as wood, where the washers springiness & sharp edges could actually work.
The evidence against split washers started stacking up in the &#;s when a gentleman named Gerhard Junker published some of his lab experiments. He invented a machine specifically for testing the effect of vibrations on threaded fasteners. The first thing he discovered was that transverse vibration loads generate a much greater loosening effect than do axial vibrations. Good to know.
His second discovery was made by plotting the bolt tension vs vibration cycles to create a &#;preload decay chart&#;. When he compared the preload decay of a bolt & split washer combo to bolt by its lonesome, he found that the split washer caused the connection to loosen sooner, as seen below.*
Not to worry, there are better locking options available. Chemical lockers like Loctite, deformed thread lock nuts, and Nyloc nuts should be your everyday go-to locking devices. If you have some money to burn then wedge lock (Nord-lock) washers &
Serrated flange nuts are probably the best way to go.
For more Friction Boltinformation, please contact us. We will provide professional answers.
When lives are on the line you may want to employ a &#;positive locking device&#; such as a castle nut or a slotted nut. No amount of vibration will break this kind of connection:
Since this one is sure to stir things up when you mention it the guys at the office, I&#;ve provided my sources below.
A) Article 1 n boltscience.com and Article 2 on Boltscience.com and Article 3 on Boltscience.com, all condeming split washers
B) pdf file from hillcountryengineering.com condeming split washers
D) Awesome video showing actual testing and how preload decay charts are generated.
*E) Alternate Testing Video #1 making the counter argument in favor of split washers.
*F) Alternate Testing Video #2 making the counter argument in favor of split washers.
.
#2. Double Nutted joints with jam nuts are affected by order of clamping. While I&#;m talking about bolt locking techniques, I&#;ll share another interesting one: For double nut connections involving the use of a jam nut & a standard nut, it REALLY matters what order you install them in.
The jam nut should go on first! Otherwise the effectiveness of the nut pair is greatly reduced. Double nut Source.
Before I move on to the next one I need to clarify the difference between static loads and fatigue loads. Static loads do not change over time. If a bolt is rated to yield at 3,000 lbs of tension, any static load less than that will not have a permanent effect.
However, if you were to vary that applied load over time you can fatigue the bolt until it breaks using less than 3,000 lbs! In the same way that a small stream can carve out the Grand Canyon, fatigue loads gradually chip away at the structural integrity of fasteners over time.
#3. The relationship between fatigue load and the number of cycles until bolt failure occurs can be predicted using experimentation. It turns out that you can make reasonably accurate predictions of the cycle count at failure by performing as few as three experiments (though I would recommend doing at least 6 to attain some real accuracy). All it takes are a few data points and a regression line to create a high cycle fatigue life curve (aka an S-N curve).
We don&#;t put the ultimate static loading on the graph, but if we did it would be the highest point on the &#;applied load&#; axis and the zero point on the &#;cycles&#; axis.
Why is this useful? Now that you know bolts can break from small fatigue loads, imagine trying to build a bridge using riveted or bolted connections. How could you trust that you ever had a big enough fastener? It turns out that fatigue loads below a certain threshold will never cause the fastener to break.
As a very general estimate, a bolt will require an infinite number of cycles to break if the fatigue load is around 30% (+/-15%) of the ultimate static load. You can expect the bolt to break in a few thousand cycles if the fatigue load is about 80% (+/-10%) of the ultimate static load. (Note: the exact percentage can vary dramatically based on material composition and ambient conditions.)
#4. (UPDATED) For maximum strength tighten bolts up to the yield point&#;For maximum durability, don&#;t! There is a common misunderstanding that a bolt within a securely fastened connection is impervious to outside forces if hey don&#;t exceed the clamped load of the connection.
That is, the myth says a bolt clamped to 500 lbs won&#;t experience additional stress unless outside forces applied to the clamp exceed 500 lbs. This is not so! In fact ANY additional load, no matter how small, will add to the tension in the bolt. But not at a 1:1 rate.
Think of pulling on a fastened connection as if it were 2 stacked springs. Both springs stretch measurably, but the weaker one stretches more. Part of the external load is absorbed by the joint and part by the fastener.
To be crystal clear, as you tighten the nut the bolt will compress the two parts together. The bolt itself has an internal reaction force equal to the amplitude of the compression force, but the bolt itself is in tension. If you were to graph the tension on the bolt while you tighten the nut, the plot would look like the graph below. To get the greatest clamping force out of the bolt we would to tighten it all the way up to the yield point. Any more force and the bolt will enter the plastic region and permanently deform.
In practice engineers don&#;t design that way. Since any additional force will begin to yield the bolt, you want to give yourself some margin for error. Engineers select a bolt tension that is somewhere between the calculable minimum functional clamping force and the yielding force&#;. while also accounting for error in the tension measurement method.
(Sources: Shingley&#;s Standard Handbook & Article on Fastenal )
#5. It is actually quite difficult to determine the exact load the fastener sees during clamping. We now know how important it is to avoid over tightening a bolt, but how do we know when it is yielding?
For everyday purposes the clamping force can be approximated by measuring the tightening torque. You can look up the recommended tightening torque for a given fastener size in my bolt sizing calculator or in a table like the one found here. An alternate method is called the &#;turn of the nut&#; wherein you tighten the bolt until it &#;feels snug&#; before rotating it another 90 degrees to ensure adequate tightness.
Those methods work OK for most things, but some critical applications require you to be certain of the clamping force (think spacecraft or large weights above your head). The torque method has difficultly accounting for friction and lubrication, but at least the torque is mathematically correlated to the clamping force. On the other hand the turn of the nut method uses rotational displacement to bypass lubrication affects, but it doesn&#;t even consider forces at all.
There are better options though. Load indicating washers can accurately verify bolting loads by squishing open a paint sack after reaching a specific load. The drawback with these is that they only work once. http://www.boltscience.com/pages/tighten.htm The other option comes from a company called smart bolts who came out with a fastener featuring a built-in tension indicator. This is by far the most accurate method of measuring bolt clamping load. On the other hand, a single box of these bolts can cost around 10 times as much as a standard fastener!
Neat, I just wish I could afford one.
How different tightening methods compare in terms of accuracy.
#6. If you&#;ve ever designed a part with a threaded hole, you may have wondered:&#;How many threads do I need to make a strong connection?&#; The answer is that it varies, but six at most.
Bolts actually stretch very slightly when force is applied, which causes the loading on each thread to be different. Because of this stretch, when you apply a tensile load on a threaded fastener the first thread at the point of connection sees the highest percentage of the load. The load on each successive thread decreases from there, as seen in the table below.
Additional threads beyond the sixth will not further distribute the load and will not make the connection any stronger.
So will a bolt break before the nut strips? Yes! Nuts typically have no less than three internal threads, but nut thickness standards have been selected on the basis that the bolt will always sustain tensile fracture before the nut will strip.
#7. Have you ever seen a fastener labeled with a 2A or 3B rating and wondered what that meant?That number-letter combo is used to indicate the thread class of the fastener. Thread classes include 1-4 (loose to tight), A (external), and B (internal). These ratings are clearance fits which indicates the level of interference during assembly.
- Class 1 is a good choice when quick assembly and disassembly is a priority.
- Class 2 is the most common thread class because it offers a good balance between price and quality.
- Class 3 is best used in applications requiring close tolerances and a strong connection.
- Class 4 is precision tight, typically used for lead screws and such.
#8. All fasteners are available with either coarse or fine threads and each option has its own distinct advantages.
Finely threaded bolts have slightly larger cross-sectional areas than coarse bolts of the same diameter, so if you are limited on the bolt size due to dimensional constraints, choose a fine thread for greater strength. Fine threads are also a better choice when threading a thin walled member. When you don&#;t have much depth to work with, you want to utilize their greater number of threads per inch. Fine threads also permit greater adjustment accuracy by requiring more rotations to move linearly.
On the other hand, coarsely threaded bolts are less likely to be cross threaded during assembly. They also allow for quicker assembly and disassembly, so choose these when you will be reassembling a part often. If the threads will be exposed to harsh conditions or chemicals, a coarsely threaded fastener should be considered for its thicker plating/coating. Coarse ly threaded fasteners are much more commonly available in the united states.
#9. Would you expect a bolt to be stronger or weaker at very high temperatures? How about at cryogenic temperatures?
Most people answer &#;weaker&#; to both question, but being weaker at both temperatures doesn&#;t even make sense when you think about it. Why would steel be strongest at whatever typical room temperature happens to be? It&#;s not.
As a rule, metals are strong & brittle at low temperatures and soft & ductile at high temperatures, within their solid phase temperature range. Room temperature is just another non-extreme point on the curve.
#10. You can make bolted connections more resistant to shear loads by using clever design instead of larger bolts. For maximum strength, try to use the correct thread length for the connection. In the image below you can see two connections which are identical except that the one on the right has a properly sized thread length. It exposes the bolt shank (rather than the threads) to the applied load at the connection seam.
All else remaining the same, the connection on the right will be stronger because the shank has a larger cross-sectional area and no stress concentrations.
Another clever trick is to design connections so that the applied load will be on multiple sections of the bolt, as opposed to just one section. In the images below there are two connections. The one on the right is twice as strong as the one on the left because it would have to shear the bolt off in two places to become free. Also, the single shear configuration can also lead to bending loads on the fastener and loosening of the connection (see #1).
#11. Have you ever cursed the day you were born because you just stripped out a Phillips head screw? While it is nice that Phillips screw drivers don&#;t slip off screws like flat heads do, it&#;s a real pain when the head can no longer be rotated because the screw head has melted into a hollow cone.
As frustrating as that is, it turns out that Phillips head screws are designed to strip out via the tapered point and rounded edges. The technical term is called a cam-out and every time it happens the relative surface motion wears out your screw. Alternate screw heads like torx and pozidriv are specifically designed not to cam-out.
..
If fascinating facts about fasteners are your thing then you should check out Carroll Smith&#;s &#;Nuts, Bolts, Fasteners, and Plumbing Handbook&#; aka &#;Screw to Win&#;. Smith&#;s Engineer To Win is another good one. Actually every book by Carroll Smith is pure gold.
You might also enjoy reading about a custom MS Excel based EngineerDog Bolt Sizing Calculator here.
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