DIN 7991 Flat Head Countersunk Socket Cap Screw Grade 10.9 Zinc CR3

FULLERKREG DIN 7991 / ISO 10642 Grade 10.9 Zinc CR3 Flat Head Countersunk Socket Cap Screws

FULLERKREG DIN 7991 / ISO 10642 Grade 10.9 Zinc CR3 Flat Head Countersunk Socket Cap Screws are high-strength fasteners featuring a 90° countersunk flat head with a hexagon socket drive. Manufactured from 10B21 boron-alloyed steel with an electroplated zinc CR3 (trivalent chromate) surface treatment, these screws combine Grade 10.9 tensile strength (min. 1,040 MPa) with a flush-fit profile, reliable corrosion resistance, and full RoHS environmental compliance. The bright silver zinc finish provides a professional appearance while the countersunk head sits flush with or below the mating surface, making these screws ideal for high-strength, RoHS-regulated, and corrosion-exposed flush-fit applications.

Product Specifications

• Standards: DIN 7991 / ISO 10642
• Strength Grade: 10.9 (heat treated)
• Material: 10B21 boron-alloyed steel
• Tensile Strength: Min. 1,040 MPa
• Yield Strength: Min. 940 MPa
• Hardness: HRC 32–39
• Head Type: Flat countersunk head, 90° included angle
• Surface Treatment: Zinc electroplating with CR3 trivalent chromate passivation
• Plating Thickness: Typically 5–12 μm zinc
• Salt Spray Resistance: 24–48 hrs (per ISO 9227)
• RoHS Compliance: ✅ Fully compliant — CR3 trivalent chromate contains no hexavalent chromium (Cr6+)
• Thread Type: Metric coarse, full thread
• Thread Tolerance: 6g
• Drive Type: Hexagon socket (Allen key / hex key)
• Sizes Available: M3 – M20

RoHS Compliance — CR3 Trivalent Chromate Zinc Plating

The zinc CR3 coating uses trivalent chromium (Cr3+) passivation, replacing the traditional hexavalent chromium (Cr6+) process. This is essential for compliance with international environmental regulations:

Regulation	Requirement	CR3 Zinc Compliance
EU RoHS Directive (2011/65/EU)	No hexavalent chromium (Cr6+)	✅ Compliant
EU REACH Regulation	No SVHC restricted substances	✅ Compliant
ELV Directive (2000/53/EC)	No Cr6+ in vehicle components	✅ Compliant
China RoHS (GB/T 26572)	No restricted hazardous substances	✅ Compliant

Surface Finish Comparison — Zinc CR3 vs Black Oxide

Property	Zinc CR3 (This Page)	Black Oxide
Appearance	Bright silver	Matte black
Coating thickness	5–12 μm	1–2 μm
Salt spray resistance	24–48 hrs	Low (without oil)
RoHS compliance	✅ Compliant (CR3)	✅ Compliant
Countersink fit impact	Minimal (5–12 μm)	Negligible (1–2 μm)
Best for	Outdoor, humid, RoHS-regulated applications	Indoor, general industrial
Price	🔵 Slightly higher	🟢 Economy

Material — 10B21 Boron Steel Chemical Composition (%)

FULLERKREG DIN 7991 Grade 10.9 Zinc CR3 countersunk screws are manufactured from 10B21 boron-alloyed steel. The addition of boron (B) significantly improves hardenability, enabling Grade 10.9 mechanical properties with a leaner alloy composition. All values are maximum unless a range is indicated.

Grade	C	Si (max)	Mn	P (max)	S (max)	B
10B21	0.18–0.23	≤0.30	0.80–1.10	≤0.030	≤0.030	0.0005–0.003

Mechanical Properties — Grade 10.9 (ISO 898-1)

Property	Requirement	Unit
Tensile Strength (Rm)	Min. 1,040	MPa
Yield Strength / Proof Load Stress (Rp0.2)	Min. 940	MPa
Core Hardness	32–39	HRC
Surface Hardness (max)	≤44	HRC
Elongation after fracture (A)	Min. 9	%
Reduction of area (Z)	Min. 48	%
Impact energy (KV) at room temp.	Min. 37	J
Head Angle	90°	degrees
Thread Tolerance Class	6g	—
Surface Treatment	Zinc CR3 (trivalent chromate)	—

Key Features

• ✅ RoHS & REACH Compliant — CR3 trivalent chromate zinc plating contains no hexavalent chromium (Cr6+), meeting EU RoHS, REACH, ELV, and China RoHS requirements
• Flush-fit countersunk head — 90° flat head sits flush with or below the mating surface, eliminating protrusions for a clean, snag-free finish
• Grade 10.9 high strength — 1,040 MPa tensile strength, 49% stronger than A2-070 stainless (700 MPa)
• Zinc CR3 coating — bright silver appearance with 24–48 hours salt spray resistance (ISO 9227)
• 10B21 boron steel — excellent hardenability and consistent mechanical properties through heat treatment
• DIN 7991 / ISO 10642 dual standard — internationally recognized specification
• ISO/TS16949 quality management — hardness test, tensile test, salt spray test, and PPAP report available on request

Applications

FULLERKREG DIN 7991 Grade 10.9 Zinc CR3 countersunk socket cap screws are widely used in high-strength, RoHS-regulated, and corrosion-exposed flush-fit applications:

• Electronics and electrical equipment (EU RoHS regulated) requiring flush fasteners
• Automotive body panels and EV (electric vehicle) assemblies (ELV compliant)
• Outdoor machinery and equipment requiring corrosion-resistant flush fasteners
• Robotics and automation equipment in humid environments
• Bicycle frames, motorcycle components, and sporting equipment
• Consumer electronics and home appliances with flush-fit requirements
• Industrial fixtures and structural connections requiring flush fasteners
• Any application requiring Grade 10.9 countersunk screws with RoHS-compliant zinc plating

Countersunk Hole Requirements

• Countersink angle: 90° included angle (standard metric countersink)
• Countersink diameter: Must match or slightly exceed the screw head diameter (dk) to allow flush seating
• Plating note: Zinc CR3 plating (5–12 μm) has minimal effect on head dimensions. For precision countersink fits, verify head diameter after plating against your countersink diameter
• Material consideration: In soft materials (aluminum, plastic), the countersink may deform under high torque — reduce torque or use a larger head diameter

Dimensional Specifications — DIN 7991 / ISO 10642 (Unit: mm)

Thread (d)	Pitch (p)	Head Dia. dk Max.	Head Dia. dk Min.	Head Height k Max.	Head Height k Min.	Key Size s	Key Depth t Min.	Body Dia. ds Max.	Body Dia. ds Min.
M3	0.5	6.72	6.48	1.86	1.66	2.0	1.1	3.00	2.86
M4	0.7	8.96	8.62	2.48	2.18	2.5	1.5	4.00	3.82
M5	0.8	11.20	10.82	3.10	2.72	3.0	2.0	5.00	4.82
M6	1.0	13.44	13.02	3.72	3.32	4.0	2.5	6.00	5.82
M8	1.25	17.92	17.42	4.96	4.46	5.0	3.5	8.00	7.78
M10	1.5	22.40	21.82	6.20	5.52	6.0	4.4	10.00	9.78
M12	1.75	26.88	26.22	7.44	6.64	8.0	5.3	12.00	11.73
M16	2.0	33.60	32.82	8.80	7.90	10.0	6.8	16.00	15.73
M20	2.5	40.32	39.42	10.16	9.06	12.0	8.2	20.00	19.67

Frequently Asked Questions

Q: What is the difference between Zinc CR3 and traditional yellow zinc (Cr6+)?
Traditional yellow zinc chromate uses hexavalent chromium (Cr6+), which is restricted under EU RoHS and REACH regulations. Zinc CR3 uses trivalent chromium (Cr3+), providing equivalent corrosion protection without any restricted substances. CR3 is the environmentally compliant replacement.

Q: What countersink angle is required for DIN 7991 screws?
DIN 7991 uses a 90° included angle countersink, which is the standard metric countersink angle. Ensure your countersink tool or pre-drilled hole uses a 90° angle for correct flush seating.

Q: Does the zinc CR3 plating affect the countersink fit?
Zinc CR3 plating is 5–12 μm thick, which has minimal but non-negligible effect on head dimensions compared to black oxide (1–2 μm). For precision countersink fits, verify the plated head diameter against your countersink diameter before assembly.

Q: Can I get RoHS compliance documentation?
Yes. FULLERKREG provides RoHS compliance declarations, PPAP reports, material certificates, and test reports upon request for all zinc CR3 plated products.

Q: What corrosion resistance does Zinc CR3 provide?
Zinc CR3 plating provides 24–48 hours of salt spray resistance (per ISO 9227) before red rust appears, depending on plating thickness.

Packaging & Availability

• Standard sizes M3 – M20 available in stock
• Bulk carton packaging; small box and custom packaging available
• RoHS compliance documentation and material certificates available on request
• PPAP report and test reports available on request
• Custom lengths accepted for large orders

Download Specification

• DIN 7991 / ISO 10642 — Full Dimensional Specification (PDF)
• ISO 898-1 — Mechanical Properties of Fasteners (PDF)

Quality Assurance

All FULLERKREG DIN 7991 Grade 10.9 Zinc CR3 countersunk socket cap screws are manufactured under strict quality control procedures including:

• Rockwell hardness test (HRC 32–39)
• Tensile strength test (min. 1,040 MPa)
• Salt spray corrosion test (zinc CR3, 24–48 hrs per ISO 9227)
• RoHS substance verification — no hexavalent chromium (Cr6+)
• Head angle verification (90° countersink)
• Dimensional inspection per DIN 7991 / ISO 10642
• Chemical composition analysis (10B21, B content verified)
• PPAP documentation available upon request

For wholesale pricing, bulk orders, RoHS documentation, or technical inquiries, please contact our sales team.