Allen screws 4×20 aisi 316 – code: a4-7991-04×020 – Osculati

Allen screws 4×20 in AISI 316 stainless steel Osculati (code a4-7991-04×020)

The Allen screws 4×20 Osculati in AISI 316 stainless steel (code a4-7991-04×020) are screws with countersunk head with hex socket, designed for fastenings where it is important to achieve a flush mounting and a clean finish, without protrusions. The countersunk head geometry is particularly useful when the screw must integrate into the component, reducing external bulk and facilitating coupling with other elements.

This type is commonly associated with standards DIN 7991 / UNI 5933, a widespread reference for countersunk head screws with hex socket. The use of’AISI 316 makes it a frequent choice in nautical and humid environments, where stainless steel fastenings are preferred to limit oxidation phenomena and maintain an orderly appearance of the hardware over time.

Features and construction details

Countersunk head: flush fastening and neat finish

The countersunk head allows the screw to fit into the designated seat, achieving a flush result with the surface. This approach is useful when:

• you want a finish without protrusions on panels, brackets, or accessories;
• you want to reduce the risk of bumps or snags on protruding parts;
• it is necessary to keep space free for coupling with other components.

Hex socket: practical tightening in maintenance

The’hexagonal recess (Allen key) is appreciated in technical assemblies and maintenance interventions because it allows controlled tightening and easy access even in spaces where traditional tools may be less practical. In onboard contexts, where work is often done on installed components not always easily reachable, the hex socket represents a functional solution.

AISI 316 stainless steel: common choice for humid environments

The’AISI 316 it is a material frequently used in nautical applications and in environments exposed to moisture and weather agents. In general, the use of stainless steel screws is preferred when you want to reduce the need for replacements due to oxidation and maintain good aesthetic continuity with onboard hardware.

Type references: DIN 7991 / UNI 5933

These Allen screws fall within the type commonly referred to as DIN 7991 / UNI 5933, associated with countersunk head screws with hex socket. If you are making a replacement, this reference is useful to compare head shape and recess with the screws already installed.

Product identification

• Brand / supplier: Osculati S.r.l.
• Supplier product code: a4-7991-04×020
• Type: countersunk head screw with hex socket (Allen)
• Material: AISI 316 stainless steel
• Format: 4×20

Typical applications (nautical and onboard plant engineering)

Stainless steel countersunk Allen screws are often used in hardware and in assemblies where discreet and integrated fastening is required. In nautical contexts, they can be used, for example, for:

• installations and replacements on onboard components designed with countersunk seats;
• fastening of brackets, supports, and accessories where a clean external surface is desired;
• mountings on elements subject to moisture contact, where stainless steel screws are preferred; stainless steel;
• technical assemblies where access with hex key is more practical compared to other recesses.

The choice of countersunk head is particularly suitable when the component to be fastened is designed to accommodate the screw flush, avoiding protrusions that could interfere with moving parts or the aesthetics of the installation.

Usage and operational notes

Countersunk seat check

To properly use the countersunk head, it is important that the component has a compatible countersunk seat. In case of replacement, check that the previous screw was of the same type (countersunk head with hex socket) and that the new screw fits correctly without play or misalignment.

Tool selection

Use a hex key in good condition and well inserted into the socket, to reduce the risk of damaging the socket during tightening or disassembly. During maintenance, especially on exposed screws, a suitable tool helps to work more cleanly and safely.

Good practices in a nautical environment

In onboard installations, it is advisable to adopt measures consistent with the existing hardware and the paired materials. If the fastening involves different components, consider the practices normally used in boating to limit problems over time (for example in the presence of moisture or contact between different metals), choosing solutions compatible with your system and configuration.

Spare parts and quick identification

For reorders or targeted replacements, refer to the Osculati code a4-7991-04×020 and the description 4×20 AISI 316 hex keys. This helps maintain consistency between existing fastenings and new ones, especially when working on multiple points of the same installation.

FAQ – Frequently Asked Questions

Are these Allen screws countersunk or cylindrical head?

They are countersunk head screws with hex socket, designed for flush mounting when a countersunk seat is present.

Is the product made of AISI 316 stainless steel?

Yes, the screws are made of AISI 316 stainless steel, a common choice for applications in humid environments and in the nautical field.

To which type references do they correspond?

They correspond to type DIN 7991 / UNI 5933, commonly associated with countersunk head screws with hex socket.

What is the Osculati reorder code?

The supplier product code is a4-7991-04×020. Use it as a reference for reorders or replacements.

For what uses are they indicated in nautical applications?

They are suitable for installations and replacements on onboard hardware and components designed for countersunk heads, where a flush finish and tightening with an Allen key are desired.