Engineering, construction, or manufacturing projects utilizing metric fasteners require very precise measurements. Metric-based fasteners allow for the secure connection of materials via standard components and sizing, which ultimately aids in achieving performance-related attributes. Understanding typical metric-based fastening sizes, their use cases, and torque-based variables will allow for easier selection and improved likelihood of success for the project.
What are the Sizing Methods Used for Metric Fasteners?
The most common metric fastener sizes consist of three parts: diameter, thread pitch, and overall length. For instance, a fastener identified as M8 x 1.25 x 30 can be defined as follows:
- Diameter (M8): Outside diameter of the threaded section of the fastener is 8 mm.
- Thread Pitch (1.25): Distance between each of the threads is 1.25 mm.
- Length (30): Shaft length (not including head) is 30 mm.
This size convention provides standardization, as applicable, for metric fasteners throughout the world, which allows for fastener interchangeability through global industries where manufacturing occurs outside of the United States.
What Are the Standard Sizes of Metric Fasteners?
There are many standard metric size options available in terms of size and shape based on the application and the specific fastener intended to use with it. The diameter of the metric bolts we carry are generally as follows:
- Small Sizes – M3 through M6 are usually used in electronics, lightweight assemblies, and small machinery.
- Medium Sizes – M8 through M12 are commonly used in automotive and industrial applications.
- Large Sizes – M14 through M20+ are typically used in heavy equipment, construction, and large-scale manufacturing.
The diameter of the metric bolts can be mated with various pitches of threads (coarse or fine) and includes varying lengths for different installations used for mounting thickness. The choice of diameter will depend on the load requirements for the application and the specifics of your project.
Types of Metric Bolts and Their Applications
Metric bolts have many forms, used for different applications:
- Hex Head Bolts: These are the most versatile types of metric bolts and can be used for construction, automotive, or general-purpose applications.
- Socket Head Cap Screws: These metric bolts are ideal for high-strength fastening and clean and efficient design and will be found in many different industrial applications including machinery and tooling.
- Flange Bolts: These include a built-in washer-like flange on the head to distribute loading on bearing surfaces and will be used in automotive assemblies.
- Carriage Bolts: These bolts have a rounded head and a square neck which makes them well-suited for wood and light metal assemblies.
- Speciality Metric Fasteners: These include shoulder bolts, eye bolts, and U-bolts, which are manufactured for niche applications.
The type of material that the metric bolt is manufactured from also plays a role in what application it is used in, as they are commonly manufactured using stainless steel, carbon steel, or alloy steel. Fasteners manufactured from stainless steel are the best choice for use in environments exposed to moisture, as they resist corrosion, rust, and weathering.
Understanding a Metric Fastener Torque Chart
The correct installation of a metric fastener would not be complete without proper torque specifications. Inefficient torquing can contribute to bolted connections failing under fault applications (over-torquing or under-torquing). A metric fastener torque chart provides the suggested torque rating for specific sizes, materials, and grades of fasteners.
Example:
- M8 x 1.25 bolts (Grade 8.8 steel): Torque: 20-25 Nm
- M16 x 2.0 bolts (Grade A2 stainless steel): Torque: 90-100 Nm
Using a torque wrench and following the torque specifications on the metric fastener torque chart will help maintain the integrity of the system and maximize the service life of your fasteners. Always follow the manufacturer’s torque specification.
Frequently Asked Questions
What are metric fasteners used for?
Metric fasteners are used in various industries such as automotive, aerospace, construction, electronics, and machinery due to the fact that they are manufactured to international standards and are compatible with items manufactured to those dimensions.
Is it acceptable to interchange between metric and imperial fasteners?
Interchanging between metric and imperial fasteners is not recommended due to the difference in thread design and dimensions. It would be best to use the appropriate fastener type for your project to achieve the best results.
What is the best way to find a reliable supplier for metric fasteners?
If you want a manufacturer of metric fasteners that can assure you of a quality product that has the correct dimensions, you should only work with those who manufacture their fasteners following internationally recognized standards and provide documentation, such as ISO 9001 certification.
By learning about sizing, type, and torque requirements, you can create the correct design and secure assembly. When selecting and installing metric fasteners correctly, it will improve the overall performance, reliability, and durability of the fasteners you will use in your next (or current) project.
