Comprehensive Guide to M4 Screw Dimensions and Specifications

Introduction

M4 screws are popular fasteners used in a wide range of industrial and consumer applications. Understanding their dimensions is crucial for ensuring proper fit and functionality. This article provides a comprehensive overview of M4 screw dimensions, covering various aspects of their design and use.

Nominal Diameter and Pitch

• The nominal diameter of an M4 screw is 4 millimeters (mm). This refers to the approximate diameter of the screw's outer threads.
• The pitch of an M4 screw is 0.7 mm. This indicates the distance between adjacent threads.

Thread Profile: Metric Fine

M4 screws adhere to the ISO Metric Fine thread profile, characterized by:

• A thread angle of 60 degrees
• A crest radius (top of the thread) of 0.125 mm
• A root radius (bottom of the thread) of 0.125 mm

Head Types and Dimensions

M4 screws are commonly available with the following head types:

• Hex Head: Six-sided head for use with a wrench or socket
• Socket Head: Cylindrical head with an internal socket for use with an Allen key or hex driver
• Button Head: Round head with a slight dome for low-profile applications
• Flat Head: Countersunk head for flush mounting below the surface
• Pan Head: Rounded head with a flat underside for general-purpose use

Head dimensions vary depending on the head type:

Lengths and Tolerances

M4 screws are available in a wide range of lengths, typically ranging from 5 mm to 50 mm.

Dimensional tolerances are crucial for ensuring proper fit:

• Pitch Tolerance: ±0.025 mm
• Outside Diameter Tolerance: ±0.04 mm
• Length Tolerance: ±0.20 mm for lengths up to 25 mm, ±0.35 mm for lengths up to 50 mm

Materials and Coatings

M4 screws are commonly manufactured from:

• Steel: Carbon steel, alloy steel, or stainless steel for strength and durability
• Brass: For corrosion resistance and low friction
• Aluminum: For lightweight applications

Various coatings can be applied to enhance properties:

• Zinc Plating: For corrosion resistance
• Nickel Plating: For increased hardness and wear resistance
• Chrome Plating: For improved appearance and resistance to wear and corrosion

Applications

M4 screws are used in countless applications, including:

• Electronics and small appliances
• Furniture and cabinetry
• Automotive components
• Machinery and equipment

Table: Head Type Dimensions

Table: Dimensional Tolerances

Table: M4 Screw Lengths

| Length (mm) |
|---|---|
| 5 |
| 6 |
| 8 |
| 10 |
| 12 |
| 14 |
| 16 |
| 18 |
| 20 |
| 25 |
| 30 |
| 40 |
| 50 |

Stories and Learnings

Story 1: A technician was assembling a circuit board and accidentally used an M4 screw with the wrong length. The screw extended too far into the board, causing a short circuit. The technician learned the importance of carefully checking screw lengths before assembly.

Story 2: A contractor was installing a door handle and did not properly tighten the M4 screws that secured the handle to the door. The screws came loose over time, causing the handle to detach. The contractor learned the importance of using the correct tightening torque for screws.

Story 3: A hobbyist was building a model airplane and used M4 brass screws for attaching the wings. The brass screws were susceptible to corrosion, which weakened the joints over time. The hobbyist learned the importance of selecting materials that are appropriate for the intended environment.

Tips and Tricks

• Use a wrench or socket that is the proper size for the screw head to avoid damage.
• Apply a small amount of thread-locking compound to prevent loosening.
• Double-check screw lengths before assembly to ensure a proper fit.
• When tapping threads in a material, ensure that the tap is slightly larger than the outside diameter of the screw to prevent thread binding.

Pros and Cons

Pros:

• Standardized dimensions for interchangeability
• Wide availability in various materials and coatings
• Suitable for a wide range of applications

Cons:

• Potential for damage if the wrong size or length is used
• Corrosion can occur over time, especially with uncoated screws
• Can be difficult to remove if tightened excessively

Frequently Asked Questions (FAQs)

Q: What is the difference between an M4 screw and an M5 screw?
A: The M in M4 and M5 refers to the nominal diameter. An M4 screw has a nominal diameter of 4 mm, while an M5 screw has a nominal diameter of 5 mm.

Q: What is the ISO Metric Fine thread profile?
A: The ISO Metric Fine thread profile is a standard thread form used on M4 screws. It features a thread angle of 60 degrees and standardized dimensions for crest and root radii.

Q: What is the most common head type for M4 screws?
A: Hex head and socket head are the most common head types for M4 screws due to their ease of installation and wide availability.

Q: What is the recommended tightening torque for M4 screws?
A: The recommended tightening torque for M4 screws depends on the material and coating. However, a typical range is 3.0-4.5 Nm for steel screws and 2.5-3.5 Nm for brass screws.

Q: What is the importance of using the correct length of screw?
A: Using the wrong screw length can cause problems such as short circuits in electronic devices, weakened joints, or damage to the material being fastened.

Q: How can I prevent M4 screws from corroding?
A: Using coated screws or applying a protective coating yourself can help prevent corrosion. Additionally, using stainless steel screws is recommended for outdoor or wet environments.