Cap nuts, also known as blind nuts or acorn nuts, are fastening components characterized by a domed closed end that completely covers the end of the screw or stud after tightening.
Their main function is to protect the exposed threaded section from impact, dirt, moisture and external agents, while also helping to improve assembly safety by eliminating potentially dangerous protrusions.
Although they are not among the most widely used components in industrial fasteners, they are used in many mechanical and plant engineering applications where additional thread protection or a neater connection finish is required.
Characteristics of Cap Nuts
The specific closed-end geometry distinguishes cap nuts from traditional hex nuts. Once installed, the blind nut encloses the end of the screw, preventing the thread from remaining exposed to the surrounding environment.
This configuration makes it possible to reduce the risk of thread damage, limit the accumulation of contaminants and improve safety in areas accessible to operators.
For these reasons, cap nuts are often used on metal structures, machinery, industrial equipment and assemblies subject to frequent maintenance operations.
Industrial Applications of Cap Nuts
Cap nuts are used when the fastener passes completely through the component and the end of the screw would remain visible or exposed.
The most common applications include light steel structures, industrial plants, handling equipment, automatic machines and mechanical systems where it is advisable to protect the thread from impact or contamination.
In some cases, they are also selected for aesthetic or safety reasons, especially in installations where fasteners remain visible or accessible during plant operation.
DIN and UNI Standards
Cap nuts are commonly identified by the following standards:
- DIN 1587
- UNI 5721
Both standards define the main dimensional characteristics of hexagon nuts with a closed end used in mechanical and industrial applications.
Main Types
Most cap nuts available on the market follow the dimensional configurations defined by DIN 1587 and UNI 5721 standards.
In addition to standard versions, supplies can be produced with specific materials, particular threads or dedicated surface finishes according to application requirements.
Available Materials
EFS can support supplies of cap nuts in carbon steel, A2 and A4 stainless steel, alloy steels and, for specific applications, materials such as Duplex, Super Duplex, Inconel and other special alloys. Material selection mainly depends on the operating environment, the presence of corrosive agents and the required durability of the connection.
Surface Treatments
Blind nuts can be supplied with electrolytic zinc plating, hot-dip galvanizing, Geomet®, black oxide treatment, phosphating or other surface treatments compatible with the material and the expected operating conditions. Correct surface protection helps increase fastening durability and preserve thread integrity over time.
EFS Capabilities
EFS manages supplies of standard and special industrial nuts through qualified Italian and European manufacturers. On request, certified materials, dedicated treatments and technical documentation such as EN 10204 3.1 certificates can be provided, ensuring raw material traceability and compliance with project specifications.
FAQ
Are Cap Nuts and Blind Nuts the Same Thing?
Yes. The two terms identify the same component: a hexagon nut with a closed upper end designed to cover the end of the screw.
What Is a Blind Nut Used For?
It is mainly used to protect the protruding thread from impact, dirt and corrosion, while also improving assembly safety.
What Are the Reference Standards for Cap Nuts?
The most widely used standards are DIN 1587 and UNI 5721, used to define the dimensional characteristics of industrial cap nuts.
