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Flat Nuts

Advantages

PSM Flat nuts are one piece, heat treated, self-locking spring steel fasteners which provide the most inexpensive means of threaded fastening usually without the need for a spanner. They replace conventional threaded nuts and lock washers in low torque applications.

One piece application
No spanner usually
required
Vibration proof
Self locking
Non-paint clogging
Reusable

MATERIAL

CS60, CS70 carbon steel,
austempered

WHEN SPECIFYING, PLEASE STATE:

Quantity
Prefix (CBFN)
Part No.
Finish code (e.g. e.g. 2500 CBFN-0410-0)

METHOD OF ASSEMBLY:

Hold fastener over the mounting hole in exactly the same manner as conventional nut and tighten screw up to recommended torque.

Characteristics & Key Features

Flat nuts are made from spring steel grades (like CS60, CS70) with heat treatment to maintain resilience and locking behavior.
They combine nut and locking function in one piece—so you typically don’t need separate lock washers.
Vibration-proof by design, the flat nut resists loosening under cyclic loads.
They are non-clogging with paint or coatings, meaning surface finishes remain clean.
They are reusable, allowing multiple assembly cycles in many applications.
Their simple form factor makes them an economical option for moderate load applications without requiring a specialized tool.

Material Selection & Specification Guidelines

Specify the correct spring steel grade and finish for the intended environment (corrosion, wear, temperature).
Provide the flat nut prefix (e.g. CBFN) and part numbering format to match dimensions.
Indicate finish codes (e.g. 2500 CBFN-0410-0) when ordering to ensure consistency and compatibility.
When designing mating components, ensure the flat nut’s locking features (e.g. helical thread impression, earthing barbs) properly engage the screw and substrate.

Feature Code

Flat Nuts Dimensions

Installation & Use Instructions

Position the flat nut over the mounting hole just like a conventional nut.
Place the screw through the mating parts into the flat nut.
Tighten up to the recommended torque—this engages the locking feature without overstraining the nut.
Ensure the helix impressions fully seat into the screw threads for locking action.

Recommended Installation Torque

Enhance Your Assembly with Our Flat Nuts

Start browsing our products or request a quote today to find the ideal fastening solution for your application.

Frequently Asked Questions About Flat Nuts

What are Flat Nuts and what are they used for?

A: Flat Nuts (product code CBFN) are one-piece, heat-treated, self-locking spring steel fasteners that provide a low-cost, tool-free means of threaded fastening. They replace conventional threaded nuts and lock washers in low-torque applications, eliminating the need for a spanner in most cases. PSM Flat Nuts are used across automotive interior trim, appliance housings, electronic enclosures, and industrial panel assemblies wherever a compact, vibration-resistant nut is required.

How do PSM Flat Nuts (CBFN) work?

PSM Flat Nuts work by using a helical thread impression formed into the spring steel body. When a screw is tightened through the Flat Nut, the helix impressions engage the screw threads and exert a spring-loaded locking force — preventing loosening under vibration or cyclic loads. Installation is simple: position the Flat Nut over the mounting hole, insert the screw through the mating parts, and tighten to the recommended torque. No secondary lock washer is needed.

Are Flat Nuts self-locking?

Yes. PSM flat Nuts are inherently self-locking by design. The spring steel construction and helical thread impressions create a prevailing torque that resists loosening under vibration, making them suitable for applications where conventional nuts might require the addition of a separate lock washer or nylon insert to prevent backing out.

What is the difference between Flat Nuts and Cage Nuts?

U Type Nuts are designed to clip onto a specific range of panel thicknesses, determined by the spring gap of the U-shaped clip section. Installing a U Type Nut on a panel thicker or thinner than its specified range can result in a loose fit or excessive clamping stress. PSM’s dimensional data sheet specifies the panel thickness range for each U Type Nut size.

What is the difference between Flat Nuts and U-Type Nuts?

Flat Nuts (CBFN) are placed over a hole independently, like a conventional nut, and rely on their spring steel body and thread impressions for locking. U-Type Nuts (CBUN) clip over the edge or flange of a panel, positioning themselves automatically and allowing quick single-sided installation of a screw without holding a nut from the back. Use flat nuts where conventional nut placement is practical; use U-nuts where one-sided or edge-mounting is required.