M4 Mounting hole dimensions

Posted by

Introduction to M4 Mounting Holes

M4 mounting holes are a common feature in various mechanical designs, particularly in the realm of electronics and industrial applications. These holes are designed to accommodate M4 screws, which have a nominal diameter of 4 millimeters. Understanding the dimensions and specifications of M4 mounting holes is crucial for engineers, designers, and DIY enthusiasts to ensure proper fit and functionality in their projects.

What are M4 Screws?

M4 screws are metric threaded fasteners with a nominal diameter of 4 millimeters. They are widely used in assembling electronic components, mounting brackets, and securing parts in a variety of applications. M4 screws come in different lengths and head styles, such as pan head, flat head, and socket head, to suit specific design requirements.

Importance of Accurate M4 Mounting Hole Dimensions

Creating accurate M4 mounting holes is essential for several reasons:

  1. Proper Fit: Accurate hole dimensions ensure that M4 screws fit snugly into the mounting holes, providing a secure and stable connection between components.

  2. Compatibility: Adhering to standard M4 mounting hole dimensions guarantees compatibility with off-the-shelf M4 screws and other components designed to work with this size.

  3. Structural Integrity: Properly sized mounting holes distribute the load evenly and prevent excessive stress on the material surrounding the hole, minimizing the risk of damage or failure.

  4. Ease of Assembly: Consistent and precise M4 mounting hole dimensions facilitate smooth and efficient assembly processes, reducing the likelihood of misalignment or fitment issues.

Request PCB Manufacturing & Assembly Quote Now

M4 Mounting Hole Dimensions and Specifications

Basic Dimensions

The basic dimensions for an M4 mounting hole are as follows:

Dimension Value
Nominal Diameter 4 mm
Clearance Hole Diameter 4.5 mm
Tap Drill Diameter (for threading) 3.3 mm
  • Nominal Diameter: The nominal diameter of an M4 screw is 4 mm, which represents the outer diameter of the screw threads.

  • Clearance Hole Diameter: To allow for easy insertion and removal of M4 screws, the recommended clearance hole diameter is 4.5 mm. This provides a slight clearance around the screw threads, preventing binding or interference.

  • Tap Drill Diameter: When creating threaded M4 mounting holes, the tap drill diameter is 3.3 mm. This diameter is used to drill the initial hole before tapping it with an M4 thread-cutting tool.

Counterbore and Countersink Dimensions

In some cases, M4 mounting holes may require counterbores or countersinks to accommodate the screw head or create a flush surface. The dimensions for these features are as follows:

Feature Diameter Depth
Counterbore (Pan Head) 8 mm 4 mm
Counterbore (Socket Head) 7 mm 4 mm
Countersink (Flat Head) 90° Dependent on screw length
  • Counterbore: A counterbore is a shallow, flat-bottomed hole that allows the screw head to sit below the surface of the material. The counterbore diameter and depth vary depending on the screw head style, such as pan head or socket head.

  • Countersink: A countersink is a conical recess that allows flat head screws to sit flush with the material surface. The countersink angle is typically 90°, and the depth depends on the length of the screw used.

Material Thickness Considerations

When designing M4 mounting holes, it’s important to consider the thickness of the material being used. The minimum recommended material thickness for M4 screws is 2 mm to ensure sufficient thread engagement and structural integrity. However, thicker materials may be required depending on the specific application and loading conditions.

Creating M4 Mounting Holes

Drilling Clearance Holes

To create clearance holes for M4 screws, follow these steps:

  1. Select a drill bit with a diameter of 4.5 mm.
  2. Mark the desired hole locations on the material surface.
  3. Securely clamp the material to prevent movement during drilling.
  4. Drill the holes perpendicular to the material surface, ensuring a clean and burr-free finish.
  5. Deburr the holes if necessary to remove any rough edges.

Tapping Threaded Holes

When creating threaded M4 mounting holes, use the following procedure:

  1. Drill a pilot hole using a 3.3 mm diameter drill bit.
  2. Select an M4 tap with the appropriate thread pitch (0.7 mm for standard M4 screws).
  3. Apply cutting fluid or lubricant to the tap to reduce friction and improve thread quality.
  4. Align the tap perpendicular to the material surface and begin turning it clockwise while applying gentle pressure.
  5. Continue turning the tap until the desired thread depth is achieved.
  6. Reverse the tap counterclockwise to remove it from the hole, clearing any chips or debris.
  7. Clean the threaded hole to remove any remaining cutting fluid or debris.

Adding Counterbores or Countersinks

If counterbores or countersinks are required, follow these additional steps:

  1. For counterbores:
  2. Select a counterbore tool with the appropriate diameter (8 mm for pan head, 7 mm for socket head).
  3. Drill the counterbore to the specified depth (typically 4 mm) using the clearance hole as a guide.

  4. For countersinks:

  5. Select a 90° countersink tool that matches the screw head angle.
  6. Align the countersink tool with the clearance hole and drill until the desired depth is reached, creating a smooth, conical recess.

Design Considerations and Best Practices

Hole Placement and Spacing

When designing M4 mounting holes, consider the following guidelines for hole placement and spacing:

  • Ensure sufficient space between holes to maintain material strength and prevent stress concentrations.
  • Avoid placing holes too close to the edges of the material to prevent weakening or cracking.
  • Consider the size and shape of the components being mounted and provide adequate clearance for assembly and maintenance.

Material Selection

Choose materials that are suitable for the intended application and compatible with M4 screws. Common materials include:

  • Metals: Aluminum, steel, brass, and stainless steel
  • Plastics: ABS, polycarbonate, nylon, and acrylic
  • Composites: Fiberglass, carbon fiber, and laminated sheets

Consider the material’s strength, durability, and resistance to environmental factors such as temperature, humidity, and corrosion.

Screw Selection

Select M4 screws based on the specific requirements of your application, such as:

  • Length: Choose screws that provide sufficient thread engagement without protruding excessively.
  • Head Style: Use pan head, flat head, or socket head screws depending on the desired appearance and mounting configuration.
  • Thread Pitch: Standard M4 screws have a thread pitch of 0.7 mm, but finer or coarser pitches may be available for specialized applications.
  • Material: Select screw materials that are compatible with the mounting hole material and suitable for the environment (e.g., stainless steel for corrosive conditions).

Torque and Assembly

When assembling components using M4 screws, follow these guidelines:

  • Use the appropriate torque settings to prevent over-tightening or damaging the screws or materials.
  • Refer to the manufacturer’s recommendations or industry standards for specific torque values based on the screw material and application.
  • Use thread-locking compounds or lock washers to prevent loosening due to vibration or thermal cycling, if necessary.

Common Applications of M4 Mounting Holes

M4 mounting holes are widely used in various industries and applications, such as:

  1. Electronics: Mounting Circuit Boards, sensors, displays, and enclosures.
  2. Automotive: Securing brackets, panels, and components in vehicles.
  3. Robotics: Assembling frames, actuators, and sensors in robotic systems.
  4. Industrial Machinery: Fastening machine parts, guards, and accessories.
  5. Consumer Products: Assembling furniture, appliances, and household items.

Frequently Asked Questions (FAQ)

  1. Q: Can I use M4 screws in imperial-sized mounting holes?
    A: While it’s possible to use M4 screws in imperial-sized holes with close tolerances, it’s not recommended. Mixing metric and imperial sizes can lead to fitment issues and compromise the integrity of the connection. It’s best to use screws and holes that are designed to work together.

  2. Q: What if I need a mounting hole size that is not a standard M4 size?
    A: In cases where a non-standard hole size is required, you may need to create a custom solution. This could involve using a different screw size, modifying the component design, or using additional hardware such as washers or spacers to accommodate the necessary dimensions.

  3. Q: How do I choose the appropriate screw length for my M4 mounting holes?
    A: The screw length depends on the thickness of the materials being fastened and any additional components like washers or spacers. As a general rule, the screw should engage at least 2-3 threads beyond the thickness of the material. Refer to screw length charts or consult with the manufacturer for specific recommendations.

  4. Q: Can I use M4 screws in plastic components?
    A: Yes, M4 screws can be used in plastic components, but it’s important to consider the material properties and design guidelines. Use self-tapping screws or threaded inserts for better grip and to prevent damage to the plastic. Be mindful of the torque applied to avoid over-tightening and stripping the threads.

  5. Q: How do I prevent M4 screws from loosening over time?
    A: To prevent M4 screws from loosening, you can use thread-locking compounds, lock washers, or nylon-insert lock nuts. These methods help to resist vibration and maintain the tightness of the connection. Additionally, ensure that the screws are tightened to the appropriate torque specification.


Understanding M4 mounting hole dimensions is essential for designers, engineers, and anyone working on projects that involve fastening components using M4 screws. By following the guidelines and best practices outlined in this article, you can create accurate and reliable mounting holes that ensure proper fit, compatibility, and structural integrity.

Remember to consider factors such as material selection, hole placement, and screw specifications when designing M4 mounting holes. Consult with professionals or refer to industry standards for specific applications to ensure optimal performance and longevity.

With the knowledge of M4 mounting hole dimensions and related considerations, you can confidently design and assemble components using these versatile and widely-used fasteners.