M3 Screw Size Chart – Head Dimensions, Drive Sizes & Thread Pitch

M3 screws are the “small but everywhere” fastener. You’ll see them in electronics, light brackets, instruments, and compact assemblies where space is tight but alignment still matters. This Metric Specialties guide pulls the most common M3 head styles into one place so you can confirm head dimensions, drive sizes, and thread pitch before you grab tools or place an order.

DIN and ISO numbers are simply the standardized “shape definitions” for each head style. If your drawing calls out a DIN/ISO, it’s pointing you to a specific geometry, not a brand.

M3 Chart: Metric M3 × 0.50 (Coarse) Head Dimensions & Drive Sizes

Dimensions below are common standard values; manufacturers may vary within allowable tolerances. If you’re designing for tight clearance, always verify against the exact spec and supplier drawing.

Industry Applications for M3 Screws

M3 hardware shows up in places where designers want a compact fastener with predictable alignment:

• Electronics & Enclosures: PCBs, standoffs, small brackets, access panels
• Automation & Instrumentation: Sensors, guards, light-duty mounts, calibration fixtures
• Robotics & 3D Printing: Frames, motor mounts, belt tensioners, accessory brackets
• Medical & Lab Equipment: Housings and assemblies where space is tight and parts are modular
• Lighting & Signage: Low-profile fasteners for trim, clips, and small supports

M3 Thread Pitch Basics: Coarse vs. Fine

For most purchases and replacements, M3 coarse is the default: M3 × 0.50. Fine-pitch M3 exists (commonly M3 × 0.35), but it’s far less common in everyday fastener bins.

A quick rule of thumb when you’re tapping threads: tap drill size ≈ major diameter − pitch. So for M3 × 0.50, you’ll often see a tap drill around 2.5 mm (then confirm based on % thread, material, and tapping method).

If your parts are stripping, backing out, or “almost fitting,” pitch is usually the culprit—especially when someone swaps in a look-alike screw from a mixed shop drawer.

Choosing the Right Head And Drive for M3

When you’re picking an M3 style, think in terms of clearance + tool access + how you want the head to sit:

• Need strength and tool control? Socket cap (DIN 912 / ISO 4762) is the workhorse.
• Need a lower profile but still want a hex key? Low head (DIN 7984) is the “tight clearance” option.
• Want a smooth dome that won’t snag? Button head (ISO 7380) is common on covers and exposed surfaces.
• Need a flush top surface? Countersunk heads (ISO 10642 / ISO 7046) sit into a chamfered hole.
• Doing general assembly with a driver? Pan head Phillips (ISO 7045) is widely used in light-duty builds.

Frequently Asked Questions (FAQs)

How to measure an M3 screw (diameter, length, and pitch)

Check the major diameter first (M3 is 3 mm). Next, measure length from under the head to the tip (for most heads). Finally, confirm pitch: the common M3 pitch is 0.50 mm, meaning the threads advance 0.50 mm per turn.

What tool fits common M3 socket-drive screws?

Many M3 socket cap screws use a 2.5 mm hex key, while several low-profile/socket variants commonly use 2.0 mm. The exact drive can vary by head style, so match the tool to the standard you’re using.

What is the standard M3 thread pitch?

The most common is M3 × 0.50 (coarse). Fine pitch M3 (often 0.35) exists, but you’ll usually see it only when it’s explicitly specified.

Is M3 the same as #4–40?

They’re close in size, but not interchangeable. #4-40 is an inch-series thread with a different diameter and pitch standard than M3, so mixing them is a reliable way to cross-thread parts.

Why do my M3 screws “almost fit” but bind?

That’s typically one of three issues: wrong pitch, damaged threads, or the hole is unthreaded/undersized. If you can start the screw but it locks up after a turn or two, stop and verify the pitch before you turn a quick mistake into a permanent one.

Final Fit-and-Thread Reminder

Use the chart to confirm head style + drive size, then double-check thread pitch before installation. If you’re ordering replacements, start in the right product family on Metric Specialties (socket head cap screws, nuts, and washers) so the whole stack-up stays consistent from thread to tool to fit.