ASME B18.16.6 Flange Locking Nut Selection Guide

What Is an ASME B18.16.6 Flange Nut?

ASME B18.16.6 is the American Society of Mechanical Engineers standard for prevailing-torque lock nuts. It covers inch-series lock nuts in both nylon-insert and all-metal designs, including hex flange configurations.

The defining feature of a flange lock nut is its integrated flange design. The flange acts as a non-rotating washer, distributing clamp load evenly across the mating surface. This reduces the risk of damage to the part being fastened and minimizes loosening caused by uneven bearing surfaces. The serrated teeth on the bottom of the flange take the anti-loosening effect one step further—the teeth are angled to resist rotation in the loosening direction, delivering reliable locking performance.

The standard covers sizes from #2 through 3 inches, with both UNC (Unified Coarse) and UNF (Unified Fine) thread options.

Key Technical Features

Dual Locking Mechanism

ASME B18.16.6 flange lock nuts use a dual locking design. Nylon-insert nuts generate continuous friction through the interference fit between the nylon collar and the bolt threads, effectively preventing vibration-induced loosening. All-metal types achieve locking through thread deformation and are suitable for high-temperature applications. The serrations on the flange bite into the mating surface for a mechanical grip that further resists back-off.

Materials and Property Grades

The standard covers carbon steel and stainless steel. Carbon steel nuts are available in multiple property grades: nylon-insert types include N2, N5, and N8; all-metal types include A, B, C, F, and G. Grade G nuts are typically used with Grade 8 high-strength bolts for high-load applications. Stainless steel is widely used where corrosion resistance is required.

Advantages of the Flange Design

The flange allows the nut to spread clamp load without a separate washer. On serrated flange nuts, the teeth run in a single-direction spiral opposite to the tightening direction, creating effective resistance once the nut is tightened. Note that because the serrations mar the contact surface, these nuts are not suitable for applications where surface appearance matters, and they should not be used with a flat washer.

Detailed Application Areas

Automotive Industry

Automotive manufacturing is a core application for ASME B18.16.6 flange lock nuts. These nuts are widely used on assembly lines for Ford, Volkswagen, General Motors, Fiat, Peugeot, Mercedes-Benz, BMW, and other major brands. Specific uses include:

• Engine systems: In high-vibration environments, flange lock nuts secure engine mounts, exhaust manifolds, and other critical components

• Chassis and suspension: The anti-loosening performance of serrated flanges keeps suspension components tight through long-term vibration

• Body structure: The flange distributes load and prevents thin sheet metal from deforming during tightening

Industrial Machinery

In industrial machinery, these nuts are suited to vibration-prone environments, including:

• Food processing equipment: Stainless steel meets hygiene requirements, and the flange design is easy to clean

• Chemical equipment: Corrosion-resistant stainless steel grades work in fastening points exposed to chemicals

• Amusement rides: Reliable structural connections in high-vibration conditions

Construction and Infrastructure

Construction demands long-term reliability from fasteners. ASME B18.16.6 flange lock nuts are used in:

• Steel structure connection nodes

• Curtain wall installation systems

• Bridge accessory structures

The serrated flange provides extra anti-loosening security and reduces maintenance needs.

Electronics and Precision Equipment

In electronics manufacturing, these nuts are used where precise fastening is required. The flange design prevents damage to precision surfaces, while the nylon-insert type offers reusable locking performance.

New Energy and Transportation

Wind power equipment, solar mounting systems, and rail transportation equipment also rely on the reliable anti-loosening performance of these nuts. These applications typically face continuous vibration and outdoor exposure, placing strict demands on fastener durability.

Selection Guide

Consider the following factors when choosing ASME B18.16.6 flange lock nuts:

Summary

ASME B18.16.6 provides a complete technical specification for inch-series flange lock nuts, covering carbon and stainless steel, UNC/UNF threads, and both nylon-insert and all-metal locking mechanisms. The serrated flange design delivers reliable fastening in vibrating environments through a dual locking mechanism, with broad use across automotive, industrial machinery, construction, and electronics applications. Understanding the standard's technical features and application scenarios helps engineers make sound fastener selection decisions.