Overview

Flush nuts have one specific feature that separates them from general through-hole nuts and is dependent on the application. The overall length (or height) of a flush nut is meant to match the thickness of the panel into which it’s installed.

Application

This thin nut doesn’t provide many full threads to screw into, but the threads it does provide are far stronger than if the panel were to be directly tapped. Some larger sliding doors for display cases ride on wheel assemblies that need to fit within a flat profile to minimize the thickness of the door as well as the size of the entire case. A simple rectangular housing of sheet metal is bent around a wheel, and flush nuts allow for this thin panel to have threads strong enough to secure the wheel to the frame of the door. Different applications can use different nuts with more threads to improve strength and durability, and they don’t need to be flush with both sides of a panel.

Alternative Solutions

In an application with the same space limitations, there aren’t alternative solutions other than directly tapping the panel with threads. Given how few full threads can be made in a thin panel, along with the panel material being relatively soft, the risk of cross threading is high. It’s more cost-effective compared to including an additional part for stronger threads, but this may lead to quality problems down the line. For greater strength, a taller blind nut or through-hole standoff with more threads is a simple answer, but it would require a redesign of the assembly to accommodate this increase in size.

Common Attachment Technologies

Due to the amount of strength required in such a small amount of space, flush nuts are almost exclusively self-clinching fasteners. A secure interference fit broaching into a PCB requires enough surface area to maintain friction for pullout strength, and surface mounted (SMT) nuts naturally go above the surface, not meeting the flush requirements.

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