Hex Nuts

Hex nuts are six-sided hexagonal nuts used to tighten bolts and screws. One of the most common hex fasteners, they have internal threads that thread onto the shank of a hex head screw or other bolt. Hex nuts are often used with hex head bolts. However, its uses are not limited to hex head bolts. The hexagonal body allows for easy tightening while applying sufficient torque to the bolt joint. Hex nuts can be used with a variety of bolts. Their dimensions are defined in both metric and imperial sizes.

Hex nuts play a crucial role in construction by providing a secure and reliable fastening solution for a wide range of applications. Some of the key benefits and importance of hex nuts in construction include:
Strength: Hex nuts provide a strong and secure fastening solution that can hold objects together with great force, making them ideal for use in heavy-duty construction projects.
Versatility: Hex nuts can be used in a variety of applications, from securing lumber and metal to attaching fixtures and hardware.
Ease of Use: Hex nuts can be easily tightened or loosened with a wrench, making them a convenient and accessible fastening solution for construction projects.
Durability: Hex nuts are typically made from strong and durable materials, such as steel, which can withstand high levels of stress and strain, and can resist corrosion and wear.
Cost-effectiveness: Hex nuts are an affordable fastening solution that offer excellent value for money, making them a popular choice for construction projects of all sizes.

When discussing nut and bolt sizes, it is not only important to understand the differences between inch and metric fasteners, but to also understand which measurements are essential to determining the sizes of the nuts and bolts you need for your applications. All sizes of nuts and bolts fall into one of two main categories: standard/inch and metric . While it may seem natural to look for imperial nut and bolt sizes when searching for fasteners measured in inches, the industry does not use this term. Instead, you will find standard, inch, or U.S. fasteners. Fortunately, metric is the only industry term for fasteners measured in millimeters.

Differences Between Inch and Metric Nuts and Bolts
While the functionality and physical characteristics of inch and metric nuts and bolts are essentially the same, how they are sized is different. The sizes are communicated by key measurements, standards, and strength grade markings. The biggest difference between nut and bolt inch and metric sizes is how measurements are defined. While each type of nut or bolt will have its own set of characteristics to measure, every fastener is measured by its thread diameter and threads per inch (TPI) or thread pitch.
-Thread Measurements
Regardless of inch or metric measurements, thread diameter is defined by either the outside diameter (OD) or the inside diameter (ID) of the part:
*Outside Diameter (OD) or Major Diameter
Nuts: the distance between the roots of the threads.
Bolts: the distance between the crests of the threads.
*Inside Diameter (ID) or Minor Diameter
Nuts: the distance between the crests of the threads.
Bolts: the distance between the roots of the threads.
The OD is more commonly used in basic measurements. The thread measurement depends on the measurement system in use:
*Threads Per Inch (TPI): used to measure inch fasteners — how many threads are present in an inch of the thread length.
*Thread Pitch: used to measure metric fasteners — the distance between two thread crests, given in millimeters.

Measurement Format for Size Names
Nut and bolt size names, regardless of the measurement system, are always given as the OD followed by the TPI or thread pitch . The names within each measurement system will look slightly different.
-Inch Format
The measurement of an inch nut or bolt will be listed as the thread size — a number between one and 12 or an inch increment followed by the threads per inch (TPI). If the diameter is less than 1/4 inch, the diameter will be listed as a number between zero and 12; the larger the number, the closer it is to 1/4 inch. When the diameter is equal to or larger than 1/4 inch, it will be listed as an inch increment. The TPI, or number of threads within an inch of the thread length, will immediately follow the diameter.
-Metric Format
The thread size of a metric nut or bolt is listed as the letter "M" followed by a number that indicates the number of millimeters across the diameter and then the thread pitch.

Coarse and Fine Threads
Nut and bolt size names will sometimes also factor in whether the thread is coarse or fine. Simply put, coarse threads are thicker and farther apart from each other, while fine threads are thinner and closer together. There are a few acronymns that are used to designate each thread type:
-Standard Coarse Threads
*UNC: Unified National Coarse threads comparable to ISO metric threads
*UNRC: Unified National Coarse threads; the "R" indicates "rolled" external threads that have a rounded root contour. They are full interchangeable with UNC fasteners.
*UNJC: Unified National Coarse threads with an increased minor diameter and controlled root radius that disperses tensile strength over a broader area. Derived from a military specification (MIL-S-8879), they are designed for high stress applications. However, they are not interchangeable with other UNC fasteners.
-Metric Coarse Threads
ISO metric threads will simply use the word "coarse."
-Standard Fine Threads
*UNF: Unified National Fine threads.
*UNRF: Unified National Fine threads; the "R" indicates "rolled" external threads that have a rounded root contour. They are fully interchangeable with other UNF fasteners.
*UNJF: Unified National Fine threads with an increased minor diameter and controlled root radius that disperses tensile stress over a broader area. Derived from a military specification (MIL-S-8879), they are designed for high stress applications. However, they are not interchangeable with other UNF fasteners.
-Metric Fine Threads
ISO metric threads will simply use the words "fine" or "super fine."
Sometimes, you will see the same thread size listed twice, each with a different thread pitch or TPI next to them. For example:
*M2.3 x 0.45 vs. M2.3 x 0.4: These have the same diameter, but the thread pitch in the first measurement is larger than the second one, so the distance between threads will be bigger.
*10 - 24 vs. #10 - 32: These have the same diameter, but the TPI in the first measurement is lower than the second one, so there will be fewer threads per inch of thread length.
Because TPIs and thread pitches are calculated differently, remember the following:
*Inch Threads: A higher TPI indicates finer threads as there are more threads within an inch of thread length.
*Metric Threads: A lower thread pitch indicates finer threads as there is less space between each thread crest.

Standards
Nuts and bolts are regulated by standards, depending on their measurement system.
-Inch Standards
Most inch nuts and bolts comply with the Unified Thread Standard (UTS). The American Society of Mechanical Engineers (ASME) and The American National Standards Institute (ANSI) regulate this standard. Additionally, the Society of Automotive Engineers (SAE International) regulates standards for parts used in automotive applications. If any of the following standards apply to your nuts or bolts, you are working with inch fasteners:
*UTS: Unified Thread Standard for screw threads commonly used in the U.S. and Canada including Unified National Coarse (UNC) and Unified National Fine (UNF) threads. ASME/ANSI - Specifies screw thread properties for three classes of general purpose unified screw threads including: UN, UNR, and UNJ series fasteners.
*SAE: A standard that designates the number of threads per inch for coarse and fine American (or standard) bolts, screws, pipes, ports, and flange ports.
-Metric Standards
For metric nuts and bolts, the most common standards are:
*ISO: Strict specifications for coarse, fine, and superfine metric threads defined by the International Organization for Standardization.
*DIN: Standards defined by the German Institute for Standardization for thread styles commonly used in Europe.
-ASTM
The American Society for Testing and Materials (ASTM) standard covers both inch and metric nuts and bolts. We'll discuss how to identify the appropriate measurement system in the following section.

Strength Grade Markings
Sometimes, manufacturers mark their nuts and bolts with indentations to indicate the strength of the fastener. Different standards use different strength markings, but there are a few markings you are most likely to encounter.
-Inch Grade Markings
Inch nuts regulated by the SAE will have lengthwise lines within the circle on the top of the nut, while bolts will have lines on the bolt head moving from the center of the head outwards.
-Metric Grade Markings
If a nut or bolt shows numbers instead of line indentations to indicate their strength grade, it is a metric fastener. However, depending on the fastener's standard, metric nuts can also show a pattern of lines and dots between the circle and the sides of the nuts. Metric nuts will print these indentations outside the circle.
-ASTM Grade Markings
You may also come across bolts with alphanumeric marks, typically an "A," "B," or "F" in combination with one to four numbers. This mark could exist on its own or along with lines. This is an ASTM strength grade mark. If this mark is followed by a capital "M," that signifies that the fastener is metric. If there is no "M" present, it is an inch fastener.
Manufacturers are not required to mark their fasteners with strength grades, so this is not a guaranteed method of identifying the inch or metric designation of your fastener. Many nuts and bolts will only imprint the manufacturer's brand mark, which may be a simple letter and should not be confused with a strength grade.