DIN 551 slotted set screws with flat point

1. Standard Introduction (DIN 551)

DIN 551 is a German industrial standard that specifies the dimensions, technical specifications, and testing requirements for slotted set screws with a flat point. This standard ensures interchangeability and consistent performance for these fasteners. The "flat point" (also known as a flat tip or flat end) is a key feature, designed for applications where the screw must press against a surface without marking it or where it needs to sit securely on a flat machined area.

2. Product Description

A DIN 551 set screw is a headless fastener, meaning it is fully threaded and has no protruding head. It is driven by a single, straight slot cut across the diameter of one end. The other end is the "point" or "tip," which in this case is a flat point.

Design: Headless, fully threaded.

Drive Type: Slotted. This is a simple, traditional drive system.

Point Type: Flat. The end is perpendicular to the screw's axis and is typically chamfered to ease installation.

3. Material

These set screws are typically manufactured from steel, but the specific grade can vary based on the required strength.

Carbon Steel: The most common material, often in grades such as C45 (medium carbon steel).

Alloy Steel: Used for higher-strength requirements (e.g., grades like 35CrMo, 42CrMo).

Stainless Steel: For corrosion resistance, typically A2 (Austenitic 304) for general use or A4 (Austenitic 316) for marine or highly corrosive environments.

Other Materials: Brass or bronze may be used for specialized applications requiring non-magnetic or spark-resistant properties.

4. Surface Treatment / Finish

The surface treatment is applied to enhance corrosion resistance, appearance, or reduce friction.

Plain / Self-colour: No coating, just the raw material. Often used for stainless steel.

Zinc Plated: A common and cost-effective corrosion-resistant finish, often with a blue-bright or yellow (iridescent) appearance. It may be supplemented with a clear chromate passivation.

Black Oxide: Provides a mild corrosion resistance and a black, non-reflective finish. It also reduces light glare.

Geomet® (Dacromet): A high-performance zinc-flake coating offering excellent corrosion resistance, especially against salt spray.

5. Performance & Property Class (Grade)

The performance is defined by the Property Class (for steel) or material designation (for stainless steel).

Carbon Steel / Alloy Steel: Common property classes are:

4.8: Low strength.

8.8: Medium strength, most common for general applications.

10.9: High strength.

12.9: Very high strength (alloy steel).

Stainless Steel: Common classes are:

A2-50: Medium strength (approx. 500 MPa tensile strength).

A2-70: High strength (approx. 700 MPa tensile strength) - most common.

A4-70 and A4-80 for marine-grade stainless steel.

6. Dimensions & Size Range

DIN 551 specifies a range of nominal diameters and corresponding lengths.

Thread: The thread conforms to the standard metric (ISO) coarse thread (e.g., M3, M4, M5, etc.).

Common Nominal Diameter (d): Typically ranges from M1.6 to M24.

Common Length (l): Varies with the diameter. For example:

M3: lengths from 2mm to 20mm

M5: lengths from 4mm to 30mm

M8: lengths from 8mm to 50mm

M12: lengths from 14mm to 80mm

7. Common / Popular Sizes

The most frequently used sizes in industrial applications are:

M3 x 3, M3 x 5, M3 x 8

M4 x 5, M4 x 8, M4 x 10

M5 x 6, M5 x 8, M5 x 10, M5 x 12

M6 x 8, M6 x 10, M6 x 12, M6 x 16

M8 x 10, M8 x 12, M8 x 16, M8 x 20

8. Applications

DIN 551 flat point set screws are used to secure one component within or against another. The flat point is ideal for:

Securing Pulleys and Gears onto Shafts: The flat end provides a large contact area against the shaft, preventing slippage without damaging it.

Positioning Components: Aligning parts on a shaft or within a bore before final assembly.

Preventing Relative Rotation: Acting as a simple locking device.

Applications on Flat Surfaces: Where a cup or cone point might dig into a flat surface, the flat point distributes pressure more evenly.

General Machinery, Automotive, and Electronics Assembly.

9. Advantages

Non-Marring: The flat point is less likely to damage or dig into the contact surface compared to cone or cup points.

Good Bearing Surface: Provides a larger area of contact, which can be beneficial for holding torque on a smooth shaft.

Secure Location: Excellent for positioning components against a flat, machined shoulder.

Simplicity: The slotted drive is simple and can be used with basic tools.

Standardization: Conformance to DIN/ISO standards ensures wide availability and interchangeability.