Allen screws 4×40 aisi 316 – code: a4-7991-04×040 – Osculati

4×40 hex keys in AISI 316 stainless steel Osculati (code a4-7991-04×040)

The 4×40 hex keys in AISI 316 stainless steel Osculati are screws with countersunk head with hex socket, designed for fastenings where it is important to achieve a neat finish and a flush head with the surface. The product is identified by the supplier code a4-7991-04×040 and belongs to the family of countersunk head screws with hex socket according to UNI 5933 / DIN 7991.

In nautical and onboard plant engineering, this type of screw is often chosen for interventions of installation, maintenance and spare parts, when you want to maintain the same head geometry and the same fastening reference standard as the existing one.

Features and construction details

Material: stainless steel AISI 316

The screw is made of AISI 316 stainless steel, a common choice for technical applications where stainless steel material suitable for demanding contexts typical of nautical use is sought. For replacements and restorations, specifying the material helps maintain consistency with the already installed bolts.

Countersunk head for flush mounting

The countersunk head is designed to fit into the countersunk seat of the component, thus achieving a clean fit and a more uniform surface. This solution is useful when the head protrusion could interfere with moving parts, covers, panels, or finishes.

Hex socket (Allen) for practical tightening

The hex socket allows tightening with a hex key, a common method in technical fields for convenience in tight spaces and for managing tightening during assembly and maintenance. It is a typical choice when an internal drive is preferred over external drive solutions.

Reference standard UNI 5933 / DIN 7991

Belonging to the family UNI 5933 / DIN 7991 is a useful element for those who need to make a “like-for-like” replacement, verifying that the screw geometry (countersunk head with hex socket) is consistent with the design or the original fastening.

Product identification

• Supplier: Osculati S.r.l.
• Supplier product code: a4-7991-04×040

For orders, reorderings, and spare parts management, the supplier code is the fastest reference to reduce ambiguity among similar items.

Typical applications (nautical and onboard plant engineering)

These Allen screws are suitable for applications requiring a countersunk head screw with Allen tightening, particularly in contexts where assembly order and compatibility with countersunk seats are important aspects.

Examples of use

• Fastenings on panels and finishes where a flush head is desired.
• Onboard components and accessories that have countersunk seats and require a screw with an internal drive.
• Maintenance interventions and bolt replacement maintaining the same UNI/DIN standard as the existing fastening.
• Technical assemblies where head protrusion could be undesirable.

In general, the choice is particularly sensible when the component to be fastened is already prepared with a countersink and when you want to preserve the aesthetics and functionality of the original assembly.

Usage and notes for selection

Countersunk seat check

Before installation, it is advisable to check that the component has a countersink compatible with the screw head. Without a countersink, the countersunk head cannot rest properly and the result may not be flush with the surface.

Check the required standard

If the goal is a faithful replacement, check that the original fastening actually belongs to the family UNI 5933 / DIN 7991. This helps maintain the same head geometry and the same tightening logic.

Tool selection

For tightening, a hex key suitable for the slot is necessary. In maintenance contexts, using the correct tool helps preserve the imprint and work more neatly.

Note on compatibility and use

The product is designed for general technical uses in nautical/plant engineering fields, but final compatibility depends on the project, paired materials, and installation conditions. In case of doubt, it is good practice to compare the screw with the one to be replaced and refer to the code a4-7991-04×040 for correct identification.

FAQ – Frequently Asked Questions

What type of screw is this Osculati hex key?

It is a countersunk head screw with hex socket (hex key), belonging to the UNI 5933 / DIN 7991 family.

What is the material of the 4×40 hex keys?

They are made of AISI 316 stainless steel, indicated in the product name.

What is the purpose of the countersunk head?

The countersunk head is designed to fit into a countersunk seat and achieve a flush fastening with the surface.

How to correctly identify this item for a reorder?

The main reference is the Osculati supplier product code: a4-7991-04×040 (in addition to the store's internal SKU).

In what contexts is this screw typically used?

It is a common solution for installations, maintenance, and replacements in nautical and onboard systems, when you want to maintain the same standard and type of fastening.