What hex key (Allen wrench) size do I need for M2.5 and M3 countersunk screws?

For M2.5 hex socket screws, a 1.5mm hex key is typically required. For M3 hex socket screws, a 2mm hex key is typically required. These are standard sizes per ISO 4762 / DIN 912 tooling conventions. Always verify with the actual screw before installation.

M2.5 M3 Hex Socket Countersunk Machine Screws Black & Blue Rustproof 6–20mm

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M2.5 M3 Hex Socket Countersunk Machine Screws Black & Blue Rustproof 6–20mm

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Size: M2.5*6mm/Blue

QTY（pcs）: 1

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$1.84 USD

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M2.5 M3 Hex Socket Countersunk Machine Screws — Flush-Mount Rustproof Fasteners in Black & Blue

When a protruding screw head would snag wiring, interfere with a mating panel, or simply ruin a clean build, engineers, RC hobbyists, and electronics assemblers reach for M2.5 M3 hex socket countersunk machine screws. The 90° countersunk head sits flush with or below the surface, the internal hex drive resists cam-out under torque, and the rustproof finish keeps things looking sharp in finished assemblies.

Each screw is a metric countersunk (flat head) hex socket fastener per DIN 7991 / ISO 10642. Available in two thread diameters — M2.5 (pitch 0.45mm) and M3 (pitch 0.5mm) — and in two finish options: black oxide and blue oxide. Shaft lengths range from 6mm (≈1/4") to 20mm (≈25/32"), covering M2.5 at 6mm and 9mm, and M3 at 6, 7, 8, 10, 11, 12, 16, 17, and 20mm. Available in packs of 1, 20, 50, 80, or 100 pieces. Drive size: 1.5mm hex key for M2.5, 2mm hex key for M3.

Typical applications include drone and RC frame assembly (where M2.5 and M3 hex socket countersunk screws for carbon fiber are a standard spec), electronics enclosure fastening, PCB standoff and cover mounting, and precision instrument assembly — anywhere that flush-mount M3 Allen head screws for electronics or small-diameter countersunk hex bolts are specified.

🔩 M2.5 (pitch 0.45mm) and M3 (pitch 0.5mm) metric coarse thread per ISO 68-1. Head profile per DIN 7991 / ISO 10642 (90° countersunk). Drive: 1.5mm hex key (M2.5) / 2mm hex key (M3). Not compatible with UNC/UNF inch threads.

✅ Key Features of These M2.5 M3 Hex Socket Countersunk Machine Screws

⬇️90° Countersunk Flush-Mount Head — The flat countersunk head per DIN 7991 sits flush with or below the mating surface, eliminating protrusions that could snag wiring or interfere with panels — essential for M3 countersunk hex screws in electronics enclosures and drone frames.
🔑Hex Socket (Allen) Drive — The internal hex recess accepts a standard hex key (1.5mm for M2.5, 2mm for M3), providing higher torque transfer than Phillips or slotted drives and reducing cam-out risk in tight spaces or power tool applications.
🛡️Rustproof Surface Treatment — Both black oxide and blue oxide finishes provide a rustproof barrier suitable for dry indoor environments, electronics assemblies, and protected mechanical builds where bare steel would corrode over time.
🎨Two Finish Options: Black & Blue — Choose black oxide for a stealthy, uniform dark appearance in enclosures and frames, or blue oxide for a distinctive blue-black finish popular in RC hobby builds and precision instrument assemblies.
📐Wide Size Range: M2.5 & M3, 6–20mm — Covers the two most common small-diameter metric sizes with 11 length options from 6mm (≈1/4") to 20mm (≈25/32"), reducing the need to source multiple SKUs for a single project.
📦Flexible Pack Quantities up to 100 pcs — Available in 1, 20, 50, 80, or 100-piece packs, so you can order a single sample screw to verify fit before committing to a bulk pack of M2.5 or M3 hex socket countersunk screws for production.

📐 Technical Specifications — M2.5 M3 Hex Socket Countersunk Machine Screws

Thread Diameters	M2.5, M3
Thread Pitch	M2.5: 0.45mm \| M3: 0.5mm (ISO metric coarse)
Head Style	Countersunk flat head (90° angle)
Drive Type	Hex socket (Allen key) — 1.5mm for M2.5, 2mm for M3
Standard	DIN 7991 / ISO 10642
Finish Options	Black oxide (Black) / Blue oxide (Blue)
Rustproof	Yes — surface-treated for corrosion resistance in dry environments
Length Range (total, incl. head)	6mm (≈1/4") – 20mm (≈25/32")
Available Sizes — M2.5	6mm, 9mm
Available Sizes — M3	6, 7, 8, 10, 11, 12, 16, 17, 20mm
Pack Quantities	1, 20, 50, 80, 100 pcs
Material	Contact us to confirm
Country of Origin	Contact us to confirm

⚠️ Length Note: For countersunk screws, the listed length (L) is measured from the top of the head to the tip — the full length including the head. This differs from pan head or socket head cap screws where length is measured from under the head.

❓ Frequently Asked Questions

How do I choose the right length for a countersunk hex socket screw?

For countersunk screws, the listed length (L) is measured from the top of the head to the tip — the full length including the head. Choose a length that allows the head to sit flush with or just below the surface of the material after countersinking.

Quick inch reference: 6mm ≈ 1/4", 8mm ≈ 5/16", 10mm ≈ 3/8", 12mm ≈ 15/32", 16mm ≈ 5/8", 20mm ≈ 25/32".

What hex key (Allen wrench) size do I need for M2.5 and M3 screws?

Per standard metric hex socket conventions:

M2.5: 1.5mm hex key
M3: 2mm hex key

These are standard sizes per ISO 4762 / DIN 912 tooling conventions. Always verify with the actual screw before installation, as some non-standard products may vary.

What is the difference between the black and blue finish options?

The black finish is generally a black oxide coating that provides a uniform dark appearance and moderate corrosion resistance, commonly used in electronics enclosures and mechanical assemblies. The blue finish is typically a blue oxide (bluing) treatment that gives a distinctive blue-black appearance, popular in RC hobby builds and precision instruments. Both finishes are generally suitable for dry indoor environments. Contact us if you need clarification on the exact coating process.

Are these screws compatible with standard M2.5 and M3 metric threads?

Yes. These are standard metric coarse thread screws — M2.5 with a pitch of 0.45mm and M3 with a pitch of 0.5mm per ISO 68-1. They are compatible with standard M2.5 and M3 metric nuts, threaded inserts, and tapped holes. They are not compatible with UNC/UNF inch-standard threads. Always verify thread pitch before installation if mixing fastener sources.

How rustproof are these screws, and can they be used outdoors?

These screws are described as rustproof, which generally indicates a surface treatment providing moderate corrosion resistance suitable for dry indoor environments, electronics enclosures, and protected assemblies. For prolonged outdoor exposure, marine environments, or direct moisture contact, stainless steel fasteners are generally more appropriate. Contact us to confirm the exact material and coating for your specific application.

What countersunk head angle do these screws use, and will they fit my countersunk holes?

Metric countersunk screws per DIN 7991 / ISO 10642 use a standard 90° head angle. This is the most common countersunk angle for metric fasteners and is compatible with standard metric countersunk holes and counterbores. Always verify the countersink angle of your mating part before installation — some applications use 82° (common in inch-standard tooling) which is not compatible.

What are the most common applications for M2.5 and M3 hex socket countersunk screws?

These screws are commonly used in:

Drone and RC frame assembly (carbon fiber and aluminum frames)
Electronics enclosures and PCB cover mounting
Laptop, computer, and consumer electronics hardware
Precision instrument and optical equipment assembly
Small appliance manufacturing and repair
3D printer frame and hotend assembly

The flush-mount countersunk head and tamper-resistant hex drive make these screws a go-to choice wherever a clean, low-profile fastener is needed in tight spaces.

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