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DIN933 Hex Head Bolts: A Complete Technical & Industry Guide

Mar 27, 2026

1. What Is a DIN933 Hex Head Bolt?

s (width across flats)k (head height)l (grip length)HEX HEADSHANK / THREADDIN933Fully ThreadedHex Head Bolt
Fig. 1 — DIN933 Hex Head Bolt anatomy: key dimensional parameters s (width across flats), k (head height), and l (nominal length). All dimensions follow DIN 933 / ISO 4017 specification.

A DIN933 Hex Head Bolt is a fully threaded metric hexagon bolt conforming to the German DIN 933 standard. "Fully threaded" means the thread runs from directly beneath the head all the way to the tip — distinguishing it from DIN 931, which is partially threaded with an unthreaded shank section. The six-sided (hexagonal) head is designed to be driven by an open-end spanner, ring spanner, or socket, making it one of the most tooling-compatible fastener geometries in industrial use worldwide.

At Tuyue, DIN933 bolts form part of a broad hardware and fasteners portfolio that includes everything from stainless steel fasteners to solar mounting hardware — all manufactured and exported with traceable quality documentation.

2. Standards & Equivalents (DIN / ISO / ASME)

The DIN 933 standard was published by Deutsches Institut für Normung (DIN) and has been largely superseded by or harmonized with ISO 4017 at the international level. Understanding these equivalencies is critical when specifying fasteners across different procurement markets.

Standard Scope Notes
DIN 933 Fully threaded hex bolt, metric coarse & fine German national standard; still widely used in datasheets
ISO 4017 Hex head screw, fully threaded (metric) International equivalent; preferred in global specifications
EN ISO 4017 European adoption of ISO 4017 Applies in EU procurement and CE-marked assemblies
ASME B18.2.3.1M Metric hex cap screw (US) Near-equivalent; minor dimensional differences at head chamfer
DIN 931 Partially threaded hex bolt Not fully threaded — different application profile

References: DIN Normenausschuss Mechanische Verbindungselemente; ISO Technical Committee TC 2 — Fasteners.

Procurement Tip: When sourcing globally, specify both DIN 933 and ISO 4017 in your purchase order to avoid ambiguity. Most reputable manufacturers — including Tuyue — supply to both standards simultaneously.

3. Material Grades & Selection

Selecting the correct material grade is the most consequential decision in a DIN933 bolt specification. It determines load-bearing capacity, corrosion behavior, temperature performance, and total cost of ownership.

3.1 Carbon & Alloy Steel (Property Classes)

Defined by ISO 898-1, property classes for steel bolts encode both tensile strength and yield ratio in the class number. The two digits (e.g., "8.8") represent: first digit × 100 = nominal tensile strength (MPa); first digit × second digit × 10 = nominal yield strength (MPa).

Class Min. Tensile (MPa) Min. Yield (MPa) Core Hardness (HRC) Typical Application
4.8 420 340 — Light general assemblies
8.8 800 640 22–32 General structural, automotive
10.9 1040 940 32–39 Heavy machinery, hydraulics
12.9 1220 1100 38–44 High-cycle fatigue, motorsport

Source: ISO 898-1:2013 — Mechanical properties of fasteners made of carbon steel and alloy steel.

3.2 Stainless Steel (Austenitic)

Stainless grades are designated by material class and strength level per ISO 3506-1. The stainless steel bolts, nuts, screws, and washers range from Tuyue covers the two most important grades for international buyers:

Grade Alloy Min. Tensile (MPa) Corrosion Resistance Best For
A2-70 304 SS 700 Good (general) Indoor, food equipment, general use
A4-70 316 SS 700 Excellent (chloride) Marine, coastal, chemical plants
A4-80 316 SS 800 Excellent (chloride) Offshore, pharmaceutical, high load

Source: ISO 3506-1:2020 — Mechanical properties of corrosion-resistant stainless steel fasteners.

Design Note: A2 stainless can experience galling (thread seizure) during installation. Always apply anti-galling lubricant (e.g., molybdenum disulfide paste) when torquing A2 or A4 hex head bolts, especially above M12.

4. Tightening Torque Reference Values

DIN933 — Tightening Torque by Size & GradeGrade 8.8A2-70M69.5M823M1046M1279M16195Torque (N·m)
Fig. 4 — Indicative tightening torque values (N·m) for DIN933 hex head bolts: Grade 8.8 vs A2-70 stainless. Apply a friction coefficient (µ) of 0.12 (lubricated) or 0.14–0.20 (dry). Always verify with project-specific calculations per VDI 2230.
Size Grade 4.8 (N·m) Grade 8.8 (N·m) Grade 10.9 (N·m) A2-70 SS (N·m)
M6 4.5 9.5 13.5 8.0
M8 11 23 33 20
M10 22 46 65 39
M12 38 79 113 67
M16 95 195 280 165
M20 185 390 555 330
M24 320 670 955 570

Reference: ISO 16047 — Torque/clamp force testing of fasteners; VDI 2230 Guideline — Systematic calculation of high duty bolted joints (VDI, Düsseldorf).

Torque values are reference figures only, assuming a friction coefficient µ = 0.12 (lightly lubricated) and 90% utilization of yield strength. Actual torque must be calculated by a qualified engineer for each joint design, accounting for surface finish, washer use, and loading conditions.