What are the standard specifications and units of American fastener system?
The American fastener system typically follows the Unified Inch System for thread dimensions and the Society of Automotive Engineers (SAE) standards for strength grades. The main specifications include:
- Thread Specifications
- Unified National Coarse (UNC): This is the most common thread profile, with fewer threads per inch. It is used in general applications.
- Unified National Fine (UNF): This has more threads per inch, offering better strength in high-tensile applications.
- Unified National Extra Fine (UNEF): This is used in specific applications requiring a tighter fit.
- Thread Size: Specified by a number (e.g., #8, #10) or by diameter in inches (e.g., 1/4″, 1/2″).
- Threads per Inch (TPI): The number of threads per inch is specified (e.g., 1/4-20, meaning 1/4″ diameter and 20 threads per inch).
- Diameter
- Nominal Diameter: Fastener sizes range from small machine screws (#0, #2, etc.) to large bolts (e.g., 1″, 2″).
- Units: The diameter is typically measured in inches or fractions of inches.
- Length
- Length: Measured from the base of the head to the tip of the fastener.
- Units: Usually in inches or fractions of inches.
- Strength Grades (SAE)
Fasteners in the American system are graded according to their tensile strength. The grade is often marked on the head of the fastener:
- Grade 2: Low-strength, made of low or medium carbon steel.
- Grade 5: Medium-strength, made of medium carbon steel and heat-treated (three radial lines on the head).
- Grade 8: High-strength, made of alloy steel and heat-treated (six radial lines on the head).
- Units: Tensile strength is measured in pounds per square inch (psi).
- Head Types
Common head styles include hex (hexagonal), pan, flat, button, and round heads. These are specified by the design needs of the application.
- Material
Fasteners may be made of various materials such as carbon steel, stainless steel, brass, or nylon, depending on the application.
- Coating and Finishes
- Zinc-coated: For corrosion resistance.
- Galvanized: For greater corrosion resistance in outdoor environments.
- Units: Often measured by thickness in microns or mils (thousandths of an inch).
- Units for Torque
- Torque: Applied torque is usually measured in inch-pounds (in-lb) or foot-pounds (ft-lb) depending on the size of the fastener.
These units and standards form the foundation for fasteners used in most American industries, from automotive to construction.
Here is an illustration representing the United Inch System for fasteners, showing Unified National Coarse (UNC) and Unified National Fine (UNF) threads along with thread measurements and fastener diameters. It highlights the differences in the number of threads per inch and includes a size chart for reference.
What is the latest amendment in United Inch System?
The latest amendment in the United Inch System related to fasteners was introduced through several updates, including the release of the 12th Edition of the IFI Book of Fastener Standards in May 2024. This edition includes updates to 30 existing standards and introduces a new standard, IFI 171, which specifies thread dimensions for assembling bolts, studs, and nuts, especially in steel construction. The book consolidates standards from ASTM, ASME, SAE, and IFI, making it a valuable resource for industries relying on mechanical fastening systems.
In addition, ASME B18.24-2023 introduced updates to the Part Identifying Number (PIN) code system for fastener products, providing a standardized method for identifying threaded and non-threaded fasteners. This allows for better inventory control and part management in manufacturing.
What is Part Identifying Number (PIN) code system for fasteners?
The Part Identifying Number (PIN) Code System for fasteners, as defined in ASME B18.24-2023, is a standardized method used to assign a unique alphanumeric identifier to fastener products. This system is designed to simplify the identification, tracking, and management of fasteners in manufacturing, distribution, and maintenance environments.
Key Features:
- Unique Code Structure: The PIN is created through a specific arrangement of letters and numbers that denote various characteristics of the fastener, such as:
- Type of fastener (e.g., bolt, nut, screw)
- Thread size (e.g., 1/4″, 1/2″, etc.)
- Material (e.g., carbon steel, stainless steel)
- Finish or coating (e.g., zinc-plated, galvanized)
- Strength grade (e.g., Grade 5, Grade 8)
- Versatility: It covers a wide range of fasteners, including externally threaded, internally threaded, and non-threaded fastener products, enabling easy identification across different product categories.
- Streamlined Inventory Control: The PIN system aids manufacturers and distributors in managing their stock more efficiently by reducing the complexity of part numbers and ensuring consistency across different suppliers and products.
- Standardization: The code system ensures that fasteners can be easily identified and categorized worldwide, improving procurement processes, quality control, and maintenance routines.
The system allows for a preselected order of coding, making it easier to decode the fastener’s specifications directly from the PIN.