Partially Threaded Hexagon Bolts (DIN 931) — Grade 8.8 Carbon Steel, Bright Zinc Plated (Zinc CR3)

FULLERKREG DIN 931 Grade 8.8 partially threaded hexagon bolts are manufactured from medium carbon steel (35K) to Property Class 8.8, with a bright zinc electroplated and trivalent chromium (CR3) passivated surface finish. Grade 8.8 is the most widely specified high-tensile bolt grade in general structural and mechanical engineering — providing a minimum tensile strength of 800 MPa with excellent toughness and fatigue resistance. The Zinc CR3 finish provides good corrosion protection while meeting RoHS and ELV environmental directives by eliminating hexavalent chromium (Cr6+).

The partially threaded shank — with a smooth unthreaded grip length beneath the head — provides precise shear load transfer through the bolt body, making DIN 931 the preferred choice for structural connections, flanged joints, and machinery where the bolt passes through clearance holes and the thread engages only in the nut or tapped hole. DIN 931 is equivalent to ISO 4014.

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Product Specifications

Standard	DIN 931 ≡ ISO 4014 (Partially Threaded Hexagon Head Bolts)
Thread	Metric coarse per ISO 261 / DIN 13
Thread Coverage	Partial thread — unthreaded grip length beneath head
Head Type	Hexagon head — driven by open-end wrench, ring spanner, or socket
Material	Carbon Steel 35K (medium carbon steel)
Property Class	8.8
Surface Finish	Bright Zinc Electroplated + Trivalent Chromium (CR3) Passivation
RoHS / ELV Compliance	Yes — Cr3+ trivalent chromium, no hexavalent chromium (Cr6+)
Zinc Layer Thickness	Typically 5–8 μm
Salt Spray Resistance	≥ 120 hours to white rust (per ISO 9227)
Size Range	M6 – M64
Length Range	25 mm – 300 mm (size-dependent)
Related Standard	DIN 933 Grade 8.8 (fully threaded)  |  ISO 4014  |  ISO 898-1 (mechanical properties)

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Head Dimensions — DIN 931 / ISO 4014

All dimensions in millimeters (mm). Data per DIN 931 / ISO 4014 standard.

Thread (d)	Pitch (mm)	s — A/F (mm)	e — A/C (mm)	k — Head Height (mm)	ds — Shank Ø (mm)
M6	1.0	10	11.05	4.0	5.7
M8	1.25	13	14.38	5.3	7.64
M10	1.5	17	18.90	6.4	9.64
M12	1.75	19	21.10	7.5	11.57
M14	2.0	22	24.49	8.8	13.57
M16	2.0	24	26.75	10.0	15.57
M20	2.5	30	33.53	12.5	19.48
M24	3.0	36	39.98	15.0	23.48
M27	3.0	41	45.20	17.0	26.48
M30	3.5	46	50.85	18.7	29.48
M36	4.0	55	60.79	22.5	35.38
M42	4.5	65	71.30	26.0	41.38
M48	5.0	75	82.60	30.0	47.38
M56	5.5	85	93.56	35.0	55.26
M64	6.0	95	104.86	40.0	63.26

* s = across flats (A/F); e = across corners (A/C); k = head height; ds = unthreaded shank diameter (max). Zinc CR3 plating (5–8μm) does not affect thread fit class. All dimensions per DIN 931 / ISO 4014.

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Thread Length (b) — DIN 931 Partial Thread Reference

The threaded length b depends on bolt diameter and nominal length L. Per DIN 931 / ISO 4014:

Thread (d)	b — L ≤ 125 mm	b — 125 < L ≤ 200 mm	b — L > 200 mm
M6	18	24	—
M8	22	28	—
M10	26	32	45
M12	30	36	49
M14	34	40	53
M16	38	44	57
M20	46	52	65
M24	54	60	73
M27	60	66	79
M30	66	72	85
M36	78	84	97
M42	—	96	109
M48	—	108	121
M56	—	—	137
M64	—	—	153

* b = threaded length. Grip length = L − b − k (approximate). Per DIN 931 / ISO 4014.

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Material & Mechanical Properties

Property	Value
Base Material	Carbon Steel 35K (medium carbon steel)
Property Class	8.8
Tensile Strength (Rm)	≥ 800 MPa (d ≤ M16) / ≥ 830 MPa (d > M16)
Lower Yield Strength (ReL)	≥ 640 MPa (d ≤ M16) / ≥ 660 MPa (d > M16)
Stress Under Proof Load (Sp)	≥ 580 MPa
Hardness	245 – 335 HV
Elongation at Break (A)	≥ 12%
Surface Treatment	Zinc electroplating + Trivalent Chromium (CR3) passivation
Zinc Layer Thickness	5 – 8 μm (typical)
Salt Spray Resistance	≥ 120 hours to white rust / ≥ 240 hours to red rust (ISO 9227)
Appearance	Bright silver / light blue iridescent
Temperature Limit	Up to +150°C (zinc plating service limit; base steel rated higher)
RoHS / ELV	Compliant — no hexavalent chromium (Cr6+)
Magnetic	Yes

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Grade 8.8 vs Other Carbon Steel Grades — Strength Comparison

Property Class	Tensile Strength (Rm)	Yield Strength (ReL)	Proof Load (Sp)	Typical Use
4.6	≥ 400 MPa	≥ 240 MPa	≥ 225 MPa	Light structural, general purpose
4.8	≥ 420 MPa	≥ 340 MPa	≥ 310 MPa	General fastening, non-structural
6.8	≥ 600 MPa	≥ 480 MPa	≥ 440 MPa	Medium-duty structural & mechanical
8.8 (This Product)	≥ 800 MPa	≥ 640 MPa	≥ 580 MPa	High-tensile structural — most widely used HT grade
10.9	≥ 1040 MPa	≥ 940 MPa	≥ 830 MPa	High-load structural, automotive
12.9	≥ 1220 MPa	≥ 1100 MPa	≥ 970 MPa	Ultra-high tensile, critical joints

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Weight Reference Table (kg / 100 pcs)

Approximate weights per 100 pieces for common sizes and lengths. Based on carbon steel density (7.85 g/cm³).

L (mm)	M6	M8	M10	M12	M16	M20	M24	M30	M36
25	0.14	0.28	—	—	—	—	—	—	—
30	0.16	0.34	0.61	—	—	—	—	—	—
35	0.18	0.40	0.72	1.08	—	—	—	—	—
40	0.21	0.46	0.83	1.25	2.46	—	—	—	—
45	0.24	0.52	0.94	1.42	2.80	—	—	—	—
50	0.26	0.58	1.04	1.58	3.13	5.51	—	—	—
60	0.31	0.70	1.26	1.92	3.80	6.69	11.0	—	—
70	0.36	0.82	1.47	2.25	4.47	7.87	13.0	—	—
80	0.42	0.93	1.69	2.58	5.14	9.05	14.9	27.5	—
90	0.47	1.05	1.90	2.91	5.81	10.2	16.9	31.2	—
100	0.52	1.17	2.12	3.24	6.48	11.4	18.8	34.9	58.8
120	0.63	1.40	2.55	3.91	7.82	13.7	22.8	42.3	71.4
140	0.73	1.64	2.98	4.57	9.16	16.1	26.7	49.7	84.0
160	—	1.87	3.41	5.24	10.50	18.4	30.7	57.1	96.6
180	—	2.11	3.84	5.90	11.84	20.8	34.6	64.5	109
200	—	2.34	4.27	6.57	13.18	23.1	38.6	71.9	122
220	—	—	4.70	7.23	14.52	25.4	42.5	79.3	134
240	—	—	5.13	7.90	15.86	27.8	46.5	86.7	147
260	—	—	—	8.56	17.20	30.1	50.4	94.1	160
280	—	—	—	9.23	18.54	32.5	54.4	101	172
300	—	—	—	9.89	19.88	34.8	58.3	109	185

* Weights are approximate (kg/100 pcs) based on carbon steel density (7.85 g/cm³). Zinc CR3 plating adds negligible weight. Contact FULLERKREG for precise weight certificates.

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Typical Applications

• 🏗️ Structural steel construction — the most widely used bolt grade for structural steel connections in buildings, bridges, and civil infrastructure
• ⚙️ Machinery & equipment — precision bolted connections in industrial machinery, conveyors, and manufacturing equipment
• 🚗 Automotive & transportation — chassis, suspension, and structural connections where Zinc CR3 meets OEM surface finish specifications
• 🔧 Flanged pipe joints — flange bolting in process piping and pressure vessels in non-corrosive service
• 🏭 Industrial plant & infrastructure — general high-tensile structural bolting in protected or mildly corrosive environments
• 🏠 Construction & prefabrication — steel frame connections, curtain wall systems, and modular construction

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Frequently Asked Questions

Q: What does Grade 8.8 mean?
A: The property class designation 8.8 indicates: the first digit (8) × 100 = minimum tensile strength of 800 MPa; the second digit (8) × 10% of tensile strength = minimum yield ratio of 80%, giving a minimum yield strength of 640 MPa. Grade 8.8 is the most widely used high-tensile bolt grade in structural and mechanical engineering worldwide.

Q: What is the difference between DIN 931 and DIN 933 in Grade 8.8?
A: DIN 931 Grade 8.8 is partially threaded — smooth shank beneath the head for shear load transfer. DIN 933 Grade 8.8 is fully threaded. Choose DIN 931 for structural shear-critical connections where the smooth shank should be in the shear plane; choose DIN 933 when maximum thread engagement or grip-length flexibility is needed.

Q: What is Zinc CR3 and is it RoHS compliant?
A: Zinc CR3 refers to zinc electroplating with a trivalent chromium (Cr3+) passivation layer. Unlike older hexavalent chromium (Cr6+) yellow zinc plating, CR3 contains no hexavalent chromium — making it fully compliant with RoHS (Restriction of Hazardous Substances) and ELV (End of Life Vehicles) directives. It provides ≥120 hours salt spray resistance to white rust per ISO 9227.

Q: Can Grade 8.8 bolts be used outdoors?
A: Zinc CR3 plating provides good corrosion protection for general outdoor use (≥120h salt spray to white rust). For prolonged outdoor exposure in humid, coastal, or industrial atmospheres, periodic inspection is recommended. For marine or highly corrosive environments, specify stainless steel grades instead.

Q: How do I calculate the grip length for a DIN 931 bolt?
A: Grip length ≈ L − b − k, where L = nominal bolt length, b = threaded length (from the table above), k = head height. For example, M16 × 100: grip ≈ 100 − 44 − 10 = 46 mm.

Q: What nut and washer should I use with Grade 8.8 bolts?
A: Use Grade 8 zinc-plated hexagon nuts (DIN 934 / ISO 4032) and zinc-plated plain washers (DIN 125 / ISO 7089) to maintain material and surface finish compatibility. For structural applications, use Grade 8 structural nuts (ISO 4033 / DIN 6915) as specified by the design standard.