The nut in hardware refers to a type of typical fastener that features a threaded hole. What are the different types of nuts to choose from, and what are their applications? In this guide, we’ll get into an in-depth overview of various fastener nuts along with a size chart, metric/imperial dimension standards, and how to use them properly (installation, anti-loosening, torque, etc.).
Different Types of Hardware Nuts and Their Uses
Hardware nuts come in many different shapes and types, each designed for specific uses in machines and structures. Most nuts are hexagonal because six sides make them easy to turn, requiring only a small twist to tighten or loosen. Some nuts, like dome and acorn nuts, protect bolt threads and look neat, while wing nuts have side wings that let you twist them by hand quickly, though they aren’t good for places with vibrations. Jam nuts are thin and help stop loosening when used with a regular nut, and flange nuts spread the load evenly like a washer, often used in cars.
1. Hex Nut
A hex nut, also known as a hexagon nut or hexagonal nut, features six flat sides, which makes it easy to grip with a wrench or a socket tool. The top and bottom are flat, and inside, it has spiral threads that match the bolt’s threads. When you screw the hex nut onto a bolt, the threads lock together tightly. Using a wrench on the six sides helps you twist the nut to tighten or loosen it.
Uses:
Hex nuts are used in cars, bicycles, furniture, and buildings, basically, any place bolts are used to hold parts together.
Common Materials:
Most hex nuts are made from steel, which is strong and durable. Stainless steel is also popular because it doesn’t rust easily. Sometimes, brass or nylon-coated nuts are used to resist corrosion or for special electrical uses.
2. Heavy Hex Nut
These nuts look like regular hex nuts but are thicker and have bigger flat sides. This gives more surface area for wrenches to grip and makes the nut stronger. Because they are bigger and thicker, heavy hex nuts can handle much more pressure and force without breaking or stripping.
Uses:
They are commonly found in heavy construction projects like bridges, buildings, and big machines where strong, heavy-duty fasteners are needed.
Common Materials:
Usually made from high-strength steel or alloy steel, sometimes heat-treated for extra toughness.
3. Nylon Insert Lock Nut
This nut looks like a regular hex nut but has a small ring of nylon inside the top threads. The nylon is usually white or blue. As you screw the nut onto a bolt, the nylon ring squeezes against the bolt threads. This creates friction that keeps the nut from loosening on its own, even if the bolt vibrates or shakes.
Uses:
Used in engines, machines, and vehicles where parts move a lot and require preventing the nut from coming loose.
Common Materials:
Steel or stainless steel nut body with a nylon insert.
4. Jam Nut
A jam nut is a thinner version of a hex nut, usually about half the thickness or less. It’s often used together with a regular nut. Tighten the regular nut first, then the jam nut is tightened against it. This “jams” the nuts together to stop them from loosening.
Uses:
Great for tight spaces or when vibrations might loosen a single nut.
Common Materials:
Steel, stainless steel, and sometimes brass.
5. Nylon Insert Jam Lock Nut
Similar to a jam nut, but it also has the nylon insert inside the threads to provide extra locking power. Combines the jam nut’s space-saving design with the nylon insert’s locking ability to prevent loosening.
Uses:
Used in smaller or tight areas where vibration resistance is critical.
Common Materials:
Steel or stainless steel with nylon insert.
6. Wing Nut
A wing nut has two wide wings on opposite sides. These wings make it easy to grip and turn by hand. Because of the wings, you don’t need tools to tighten or loosen them.
Uses:
Used when you need to assemble or disassemble things quickly, such as on bike parts, clamps, or temporary fixtures.
Common Materials:
Steel, stainless steel, brass, and sometimes plastic for lightweight applications.
7. Cap Nut
A cap nut looks like a hex nut but has a closed, dome-shaped top that covers the end of the bolt. The dome protects the bolt threads and prevents injuries from sharp bolt ends.
Uses:
Used on furniture, playground equipment, or anywhere you want a finished look and safety.
Common Materials:
Steel, stainless steel, brass, or plastic.
8. Acorn Nut
Also called a dome nut, it’s similar to a cap nut but generally taller and rounder on top, resembling an acorn. Acorn nuts cover and protect the bolt end to get a safer and better looking.
Uses:
Popular on bicycles, motorcycles, and decorative applications.
Common Materials:
Steel (often chrome-plated), brass, or stainless steel.
9. Flange Nut
A flange nut has a built-in wide base (the flange) on one side, which looks like a washer but is part of the nut. The flange spreads the pressure over a larger area and prevents the nut from loosening easily.
Uses:
Common in automotive and machinery, where vibration is a problem.
Common Materials:
Steel, stainless steel.
10. Tee Nut
Looks like a flat hex nut with long, sharp spikes or prongs sticking out underneath. You push or hammer it into wood, and the spikes dig in, holding the nut firmly in place so the nut doesn’t spin when tightening.
Uses:
Used to fasten bolts into wood, such as in furniture or wooden playgrounds.
Common Materials:
Steel, often zinc-plated for rust resistance.
11. Square Nut
A nut with four flat sides instead of six. The big flat sides make it easier to hold in place with a wrench or by hand.
Uses:
Common in old machinery, electrical work, or furniture assembly.
Common Materials:
Steel, stainless steel, brass.
12. Prevailing Torque Lock Nut
A prevailing torque lock nut is a one-piece hex nut with a flat bottom and a slightly cone-shaped (conical) top. Its corners are chamfered, which means they are slightly beveled or rounded. This nut locks by slightly distorting the threads at the top inside part of the nut. This distortion creates very strong friction between the nut and the bolt threads. Because of this friction, the nut resists loosening caused by shocks, vibrations, or any movement. It is a non-reversible lock nut, meaning once tightened, it is very hard to undo without damaging the locking part. You must use a wrench or tool to tighten or loosen it; hand-turning won’t work.
Uses:
Great for high-temperature environments where nylon inserts cannot be used, such as in engines, turbines, or industrial machines.
Common Materials:
Steel, stainless steel.
13. K-Lock or Kep Nut
A hex nut with a thin, free-spinning toothed washer attached at its base. The washer’s teeth bite into the surface to stop the nut from coming loose.
Uses:
Used in automotive and machinery applications where vibration might cause loosening.
Common Materials:
Steel, stainless steel.
14. Coupling Nut
A long hexagonal nut, much longer than normal nuts, almost like a tube. It joins two threaded rods or bolts by threading onto both ends.
Uses:
Used to extend the length of bolts or threaded rods.
Common Materials:
Steel, stainless steel.
15. Slotted Nut
A hex nut with slots cut into the top surface. Used with a cotter pin that fits through the slots and a hole in the bolt to lock the nut in place, preventing it from turning. Both castle nuts and slotted nuts have slots on top and work with locking pins to prevent loosening. However, the castle nut’s top is smaller in diameter, so the cotter pin can be wrapped and pinned against the nut, making the pin less likely to stick out. Slotted nuts don’t have this feature and have the same diameter at the top as the wrenching area.
Uses:
Common in automotive steering or wheel assemblies, where safety locking is needed.
Common Materials:
Steel, stainless steel.
16. Castle Nut
Castle nuts, also called castellated nuts, are hex nuts with notches or castles cut around their top edge. These notches look like the walls of a castle, which is how they got their name. The top part of a castle nut is slightly narrower than the main body, allowing a special pin to be secured neatly. Castle nuts are used together with a cotter pin, R clip, spring pin, or safety wire. The bolt they screw onto has a hole drilled through its threaded end. After tightening the castle nut, you insert the cotter pin through the hole and through one of the nut’s slots. Then, you bend or secure the pin so the nut cannot turn or loosen, even when there is vibration or movement.
Uses:
Automotive (especially on axles), aircraft, locomotives, and other machinery, where vibration could cause regular nuts to loosen.
Common Materials:
Steel, stainless steel, sometimes plated for corrosion resistance.
What Are the Best Nuts for Vibrations?
When the components shake or vibrate a lot, nuts can slowly work themselves loose, the best nuts for stopping this are lock nuts, like nylon insert lock nuts and prevailing torque lock nuts. Kep nuts and castle nuts are also good options. These nuts resist loosening caused by vibration because they create extra friction or use physical locks to hold tight.
Which Types of Nuts Are the Best for High-Temperature Environments?
High temperatures can melt plastic parts, so nuts with nylon inserts are not good for hot places. The best nuts for high temperatures are prevailing torque lock nuts that use metal thread distortion and heavy hex nuts that are made of strong steel alloys that withstand heat and stress. These nuts keep their locking ability even in hot environments like engines or turbines.
How to Prevent Nuts from Loosening?
- Using lock nuts like nylon insert or prevailing torque nuts.
- Adding washers, such as split lock washers or spring washers, that increase friction.
- Using cotter pins with castle or slotted nuts to physically lock the nut in place.
- Applying thread-locking glue (like Loctite) that sticks the threads together.
- Tightening the nut to the correct torque so it stays secure.
What Is the Formula for the Torque of a Nut?
Torque is the twisting force used to tighten a nut. The simplified formula to calculate the torque needed to tighten a nut is the same as the bolt torque formula.
T=K×F×d
Where:
T = Torque (usually in Newton-meters or foot-pounds)
K = Nut factor or friction coefficient (depends on lubrication and materials, usually about 0.2)
F = Axial force or clamp load (force you want the bolt to hold)
d = Nominal diameter of the fastener (in meters or inches)
Which Nuts Require Specific Tools for Installation?
Most nuts just need a wrench or socket tool, but some require special tools:
- Castle nuts: Require a cotter pin plier or needle-nose pliers to install or remove the cotter pin.
- Slotted nuts: Also need special tools for cotter pins or safety wires.
- Prevailing torque lock nuts: Require a wrench with enough torque, sometimes special sockets if they’re in tight spots.
- Wing nut: Usually no tools needed, but if very tight, pliers might help.
- Tee nuts: Often hammered or pressed in, so a hammer or press tool is needed for installation.
How to Disassemble Castle Nuts and Wing Nuts?
1. Castle Nut:
- Remove the cotter pin by straightening the bent ends and pulling it out with pliers.
- Use a wrench to turn the castle nut counterclockwise to loosen and remove it.
- Always replace the cotter pin with a new one when reassembling for safety.
2. Wing Nut:
- Because wing nuts have wings, you usually can turn them by hand counterclockwise to loosen.
- If too tight, use pliers gently on the wings to help turn it.
- Turn until the wing nut can be removed.
Nut Standards for Dimensions (ISO, ASME, ANSI, DIN, BS, and More)
| Nut Types | Standard | Unit or Measurement System |
|---|---|---|
| Hex (Hexagon) Nuts | ANSI/ASME B18.2.2 | Inch (Imperial) |
| Square Nuts | ANSI/ASME B18.2.2 | Inch (Imperial) |
| Hex Nuts, Style 1 | ANSI/ASME B18.2.4.1M | Metric |
| Hex Nuts, Style 2 | ANSI/ASME B18.2.4.2M | Metric |
| Slotted Hex Nuts | ANSI/ASME B18.2.4.3M | Metric |
| Hex Flange Nuts | ANSI/ASME B18.4.4M | Metric |
| Hex Jam Nuts | ANSI/ASME B18.2.4.5M | Metric |
| Heavy Hex Nuts | ANSI/ASME B18.2.4.6M | Metric |
| Machine Screw Nuts | ANSI/ASME B18.6.3 | Inch (Imperial) |
| Prevailing Torque Hex Nuts | ANSI/ASME B18.16.3M | Metric |
| Prevailing Torque Hex Flange Nuts | ANSI/ASME B18.16.3M | Metric |
| Wing Nuts | DIN 315 A/ DIN 315 D/ ISO 5448 | Metric |
| Hex Jam Nuts / Pipe Nuts | DIN 431 | Inch (Imperial) |
| Hex Thin Nuts / Jam Nuts | DIN 439/ DIN 439 A/ DIN 439 B/ ISO 4035/ ASME B18.2.4.5M | Metric |
| Hex Nuts | DIN 555/ ISO 4034/ UNI 82144 | Metric |
| Square Nuts | DIN 557 | Metric |
| Lifting Eye Nuts | DIN 582 | Metric |
| Spring Lock Washers, Form B | DIN 127 B | Metric |
| Special Foundation Square Nuts | DIN 798 | Metric |
| Hex Nuts | DIN 934/ ISO 4032/ ASME B18.2.4.1M | Metric |
| Hex Castle Nuts | DIN 935/ ISO 7035 | Metric |
| Hex Jam Nuts / Thin Nuts | DIN 936 | Metric |
| Nylon Insert Lock Nuts / Nylock Nuts | DIN 985/ ISO 7040/ UNI 7474 | Metric |
| Dome Nylock Nuts | DIN 986 | Metric |
| Hex Domed Cap Nuts / Acorn Nuts | DIN 1587/ PN 82121 / UNI 5721 | Metric |
| Hex Nuts | DIN 2510 Form NF | Metric |
| Prevailing Torque Hex Thin Nuts | ISO 10511 | Metric |
| Prevailing Torque Hex Nuts | ISO 10512 | Metric |
| Prevailing Torque All Metal Hex High Nuts | ISO 10513 | Metric |
| Nuts for T-Slots | ISO 299 | Metric |
| Hex High Nuts | ISO 4033 | Metric |
| Hex Flange Nuts | ISO 4161 | Metric |
| Hex Nuts With Large Across Flats | ISO 4775 | Metric |
| Slotted Hex Castle Nuts, High Type | ISO 7036 | Metric |
| High Castle Nuts | ISO 7037 | Metric |
| Slotted Hex Castle Nuts, Low Type | ISO 7038 | Metric |
| Prevailing Torque Nuts with Nylon Insert / Prevailing Nyloc Nuts | ISO 7041 | Metric |
| Prevailing Torque All Metal Hex Nuts | ISO 7042 | Metric |
| Hex Nuts with Coarse & Fine Threads | ISO 8673 | Metric |
| Jam Nuts / Thin Hex Nuts With Fine Threads | ISO 8675 | Metric |
| Hex Nuts | IS 1363 Part 3/ ISO 4034 | Metric |
| Hex Nuts | IS 1364 Part 3/ ISO 4032 | Metric |
| Hex Nuts | BS 3692 | Metric |
| Hex Machine Screw Nuts | BS 4183 | Metric |
| Hex Nuts | BS 4190 | Metric |
| Hex Thin Nuts / Jam Nuts | BS 4190 | Metric |
Metric Standard Nut Sizes Chart (ISO 4032) in MM
1. Thread Pitch
Thread pitch is the distance between the threads on the inside of the nut. It tells us how tightly or loosely the nut will screw onto a bolt. A smaller pitch means the threads are closer together, making the nut turn slowly but hold tightly. A bigger pitch has threads spaced farther apart, so you can spin the nut on faster.
2. Width Across Flats
The width across flats is the distance between two opposite flat sides of the nut. Think of the nut as a little hexagon. This measurement tells you how wide the nut is from one flat side to the flat side directly across from it. This size is important because it tells you what size wrench or spanner you need to tighten or loosen the nut.
3. Width Across Corners
The width across corners is the distance from one corner of the nut to the corner directly on the opposite side. If you look at the nut from above, it looks like a hexagon with six points. This measurement is always a bit longer than the width across flats because it stretches across the nut diagonally. This helps make sure the nut can fit into places where space is measured from corner to corner.
4. Height of the Nut
The height of the nut is how tall the nut is from the bottom to the top. It’s basically the thickness of the nut. This size matters because it affects how much thread the nut can hold onto the bolt. A taller nut can grip more threads, making the connection stronger and more secure.
| Nut Size |
Thread Pitch |
Width Across Flats |
Width Across Corners |
Height of the Nut |
||
| max. | min. | min. | max. | min. | ||
| M1.6 | 0.35 | 3.20 | 3.02 | 3.41 | 1.30 | 1.05 |
| M2 | 0.4 | 4.00 | 3.82 | 4.32 | 1.60 | 1.35 |
| M2.5 | 0.45 | 5.00 | 4.82 | 5.45 | 2.00 | 1.75 |
| M3 | 0.5 | 5.50 | 5.32 | 6.01 | 2.40 | 2.15 |
| M3.5* | 0.6 | 6.00 | 5.82 | 6.58 | 2.80 | 2.55 |
| M4 | 0.7 | 7.00 | 6.78 | 7.66 | 3.2 | 2.9 |
| M5 | 0.8 | 8.00 | 7.78 | 8.79 | 4.7 | 4.4 |
| M6 | 1 | 10.00 | 9.78 | 11.05 | 5.2 | 4.9 |
| M8 | 1.25 | 13.00 | 12.73 | 14.38 | 6.80 | 6.44 |
| M10 | 1.5 | 16.00 | 15.73 | 17.77 | 8.40 | 8.04 |
| M12 | 1.75 | 18.00 | 17.73 | 20.03 | 10.80 | 10.37 |
| M14* | 2 | 21.00 | 20.67 | 23.36 | 12.8 | 12.1 |
| M16 | 2 | 24.00 | 23.67 | 26.75 | 14.8 | 14.1 |
| M18* | 2.5 | 27.00 | 26.16 | 29.56 | 15.8 | 15.1 |
| M20 | 2.5 | 30.00 | 29.16 | 32.95 | 18.0 | 16.9 |
| M22* | 2.5 | 34 | 33 | 37.29 | 19.4 | 18.1 |
| M24 | 3 | 36 | 35 | 39.55 | 21.5 | 20.2 |
| M27* | 3 | 41 | 40 | 45.2 | 23.8 | 22.5 |
| M30 | 3.5 | 46 | 45 | 50.85 | 25.6 | 24.3 |
| M33* | 3.5 | 50 | 49 | 55.37 | 28.7 | 27.4 |
| M36 | 4 | 55.0 | 53.8 | 60.79 | 31.0 | 29.4 |
| M39* | 4 | 60.0 | 58.8 | 66.44 | 33.4 | 31.8 |
| M42 | 4.5 | 65.0 | 63.1 | 71.3 | 34.0 | 32.4 |
| M45* | 4.5 | 70.0 | 68.1 | 76.95 | 36.0 | 34.4 |
| M48 | 5 | 75.0 | 73.1 | 82.6 | 38.0 | 36.4 |
| M52* | 5 | 80.0 | 78.1 | 88.25 | 42.0 | 40.4 |
| M56 | 5.5 | 85.0 | 82.8 | 93.56 | 45.0 | 43.4 |
| M60* | 5.5 | 90.0 | 87.8 | 99.21 | 48.0 | 46.4 |
| M64 | 6 | 95.0 | 92.8 | 104.86 | 51.0 | 49.1 |
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