Carriage Bolt

1 — INDUSTRY CONTEXT, TECHNICAL DEFINITION & JOINT ENGINEERING

1.1 Industry Context

Carriage bolts represent a specialized fastening solution designed primarily for non-rotational installation environments, where access to only one side of the joint is possible or where exposed threads must remain secure against tampering.

Across global industrial sectors, carriage bolts are extensively utilized in:

• Structural steel secondary connections
• Transmission tower assemblies
• Rail infrastructure
• Conveyor and material handling systems
• Heavy equipment guarding systems
• Timber-to-steel structural connections
• Petrochemical platforms using composite panels
• Offshore deck equipment and grating assemblies

Unlike hex bolts or structural bolts, carriage bolts rely on geometry-driven anti-rotation locking rather than tool engagement at the head.

For EPC contractors and mechanical engineers, carriage bolts serve as:

✔ Semi-structural fastening elements
✔ Anti-tamper exterior fasteners
✔ Load-transferring shear connectors
✔ Alignment-maintaining joint fasteners

SM Fasteners manufactures carriage bolts under controlled ISO 9001 quality systems, supporting global infrastructure, industrial fabrication, and export-grade assemblies.

1.2 Technical Definition

A Carriage Bolt is defined as:

A round-head bolt featuring a square neck beneath the head that embeds into softer material or pre-formed square holes to prevent rotation during tightening.

Fundamental Characteristics

Feature	Engineering Function
Domed Round Head	Smooth external surface, safety & aesthetics
Square Neck	Anti-rotation locking mechanism
Threaded Shank	Generates clamping force
Partial/Full Thread	Load distribution control
Nut Tightening	Single-sided installation

Unlike hex bolts, torque is applied exclusively at the nut side.

1.3 Functional Role in Assemblies

Carriage bolts are selected where:

• Bolt head must remain flush or tamper-resistant
• Surface snagging must be avoided
• Aesthetic or safety requirements exist
• Repetitive vibration environments demand anti-rotation stability

Typical joint configuration:

1.4 Load Mechanics & Force Behavior

Primary Load Modes

Load Type	Carriage Bolt Response
Tensile Load	Carried by threaded section
Shear Load	Supported by shank diameter
Clamp Load	Generated via nut tightening
Bearing Load	Transferred through square neck
Fatigue Load	Influenced by preload stability

Load Transfer Mechanism

Carriage bolts function primarily as bearing-type fasteners rather than slip-critical structural bolts.

The square neck transfers torque resistance into the joint material:$$T_{resistance} = F_{bearing} \times Neck\ Area$$

Proper seating of the square neck is essential.

1.5 Preload and Clamping Force Principles

Bolt preload creates frictional resistance between joint members.

Preload Equation

$$F = \frac{T}{K \times D}$$

Where:

• F = Preload force (N)
• T = Applied torque (Nm)
• K = Nut factor (0.16–0.22 typical)
• D = Nominal diameter (m)

Worked Example

M12 Carriage Bolt — Property Class 8.8

• Torque = 80 Nm
• Nut factor = 0.18
• Diameter = 0.012 m

$$F = \frac{80}{0.18 \times 0.012}$$

$$F = 37,037\ N$$

Resulting preload ≈ 37 kN

1.6 Torque–Tension Relationship

Preload depends heavily on friction:

Condition	Nut Factor K
Dry steel	0.20–0.22
Zinc plated	0.18
Lubricated	0.16
PTFE coated	0.14–0.15

Approximately 85–90% of torque is lost to friction.

1.7 Joint Design Principles

Engineer Selection Criteria

Design Parameter	Requirement
Hole Geometry	Square recess or deformable material
Material Hardness	Joint softer than bolt neck
Grip Length	Match unthreaded shank
Clamp Load	Prevent joint separation
Corrosion Exposure	Select coating/material
Inspection Access	Nut-side accessibility

Recommended Joint Practice

✔ Washer under nut
✔ Full square neck engagement
✔ Avoid hardened steel mating surfaces without square recess
✔ Maintain minimum thread engagement = 1 × diameter

1.8 Thread Engagement & Load Distribution

Minimum engagement:$$L_e \ge 1.0D$$

Critical for preventing:

• Thread stripping
• Fatigue cracking
• Joint relaxation

1.9 Failure Mechanisms

1.9.1 Shear Failure

Occurs when lateral forces exceed shear capacity.$$\tau = \frac{F}{A}$$

1.9.2 Fatigue Failure

Caused by:

• Insufficient preload
• Vibration
• Cyclic loading

Mitigation:

• Proper torque control
• Hardened washers
• Controlled friction coefficient

1.9.3 Square Neck Spin-Out

Common carriage bolt failure.

Causes:

• Over-sized hole
• Hard mating material
• Poor installation

Engineering solution:

• Correct hole tolerance
• Serrated or rib-neck variants

1.9.4 Hydrogen Embrittlement

Applicable to high-strength (>1000 MPa) bolts with electroplating.

SM Fasteners applies controlled baking procedures per ISO requirements.

1.9.5 Stress Corrosion Cracking

Critical environments:

• Offshore marine
• H₂S exposure
• Chloride environments

Material upgrade required:

• Duplex
• Super Duplex
• Nickel alloys

1.10 Carriage Bolt vs Other Bolts

Bolt Type	Tooling	Anti-Rotation	Typical Use
Carriage Bolt	Nut side only	Square neck	Timber/structures
Hex bolt	Both sides	No	Machinery
Structural Bolt	Controlled tension	No	Steel structures
Elevator Bolt	Flat head	Limited	Conveyors

1.11 Engineering Advantages

• Smooth exposed surface
• Reduced injury risk
• Tamper resistance
• Fast installation
• Reliable shear transfer

1.12 SM Fasteners Engineering Integration

SM Fasteners supplies carriage bolts engineered for:

• ISO global interchangeability
• EPC procurement compliance
• Traceable manufacturing batches
• Advanced alloy material availability
• Custom square-neck geometries

Manufacturing aligns with:

✔ ISO 9001 Quality Systems
✔ UKAF-aligned verification
✔ MSME certified production capability

2. PRODUCT TYPES, DIMENSIONAL LOGIC & INTERNATIONAL STANDARDS

2.1 Carriage Bolt Product Classification

Carriage bolts are engineered in multiple configurations to satisfy varying load requirements, installation environments, joint materials, and industry specifications.

Unlike general-purpose bolts, geometry variation directly influences anti-rotation performance, bearing load transfer, and long-term joint reliability.

Primary Functional Variants

Type	Description	Engineering Purpose	Typical Industries
Standard Carriage Bolt	Round head + square neck	General structural fastening	Construction, infrastructure
Short Neck Carriage Bolt	Reduced square height	Thin materials	Sheet metal assemblies
Rib Neck Carriage Bolt	Serrated neck	Hard material anti-spin	Automotive, equipment
Fin Neck Carriage Bolt	Radial fins below head	High torque resistance	Machinery guards
Dome Head Carriage Bolt	Large smooth head	Safety exposure areas	Rail, public structures
Mushroom Head Bolt	Oversized bearing head	Soft timber joints	Bridges, wooden structures
Fully Threaded Carriage Bolt	Threads entire length	Variable grip applications	OEM assemblies
Partial Thread Carriage Bolt	Smooth shank	Improved shear strength	Structural joints
Stainless Carriage Bolt	Corrosion resistant	Marine & chemical service	Offshore & petrochemical
PEEK Carriage Bolt	Polymer engineered	Electrical isolation	Electronics, chemical plants

SM Fasteners manufactures both standardized and custom-engineered geometries to meet EPC drawings and OEM specifications.

2.2 Dimensional Logic & Geometry Engineering

Carriage bolt geometry is governed by:

• Head bearing surface requirements
• Square neck torque resistance
• Thread engagement length
• Load transfer efficiency

Key Geometric Elements

Parameter	Symbol	Function
Nominal Diameter	d	Determines tensile capacity
Thread Pitch	P	Load distribution
Head Diameter	dk	Bearing area
Head Height	k	Surface stability
Square Neck Width	s	Anti-rotation locking
Square Neck Height	v	Torque resistance
Thread Length	b	Clamping capability
Overall Length	L	Grip accommodation

2.3 Standard Dimensional Specification Table (Metric Series)

(Aligned with ISO 8677 / DIN 603)

Size	Pitch (mm)	Head Dia dk (mm)	Head Height k (mm)	Square Neck s (mm)	Neck Height v (mm)	Standard Length Range (mm)
M6	1.0	16	3.3	6.5	4.1	16–120
M8	1.25	20	4.4	8.5	4.7	20–150
M10	1.5	24	5.4	10.5	5.6	25–200
M12	1.75	30	6.5	12.5	6.8	30–300
M16	2.0	38	8.0	16.5	8.8	40–350
M20	2.5	46	10.0	20.5	11.5	50–400
M24	3.0	58	12.0	24.5	14.0	60–450

SM Fasteners maintains dimensional verification through calibrated inspection systems compliant with ISO 9001 procedures.

2.4 Imperial Dimensional Series (UNC/UNF)

Size	Thread	Head Dia (in)	Square Neck (in)	Length Range (in)
1/4″	UNC	0.625	0.260	1–5
5/16″	UNC	0.719	0.323	1–6
3/8″	UNC	0.875	0.385	1–8
1/2″	UNC	1.187	0.510	1.5–10
5/8″	UNC	1.469	0.635	2–12
3/4″	UNC	1.750	0.760	2–14

2.5 Thread Forms & Tolerances

Carriage bolts support global interchangeability through standardized thread systems.

Thread Standards Table

Standard	Thread Form	Typical Region	Tolerance Class
ISO Metric	M	Global	6g
UNC	Unified Coarse	USA/Canada	2A
UNF	Unified Fine	Precision equipment	2A
BSW	British Standard Whitworth	Legacy UK	Medium
BSF	British Standard Fine	Machinery	Close fit

SM Fasteners supplies threads verified using:

• GO/NO-GO gauges
• Optical profile measurement
• SPC-controlled rolling processes

2.6 Applicable International Standards

Carriage bolts are governed by multiple global standards depending on project specifications.

Primary Standards

Standard	Description
DIN 603	Round head square neck bolts
ISO 8677	Metric carriage bolts
ISO 8678	Reduced neck carriage bolts
ASTM A307	Carbon steel bolts
ASTM F593	Stainless steel bolts
ASME B18.5	Inch carriage bolts
BS 4933	British carriage bolt specification
EN ISO 898-1	Mechanical properties
ISO 965	Thread tolerances

Interchangeability Considerations

Parameter	ISO vs ASTM
Head geometry	Slight variation
Thread tolerance	Compatible
Mechanical properties	Grade dependent
Fit-up	Generally interchangeable

Engineering verification is recommended for EPC critical assemblies.

2.7 Mechanical Property Classes

Property class selection governs load capability.

Mechanical Property Table

Property Class	Yield Strength (MPa)	Tensile Strength (MPa)	Typical Use
4.6	240	400	Light assemblies
5.8	400	500	Timber structures
8.8	640	800	Industrial structures
10.9	900	1000	Heavy equipment
12.9*	1080	1200	Special engineered use

(*Rare for carriage bolts due to neck deformation requirements.)

2.8 Proof Load & Tensile Strength Table

Size	Grade 5.8 Proof Load (kN)	Grade 8.8 Proof Load (kN)	Ultimate Tensile (kN)
M8	14	22	28
M10	22	35	45
M12	32	50	65
M16	58	91	118
M20	91	142	184
M24	131	205	265

Values aligned with ISO 898-1 calculations.

2.9 Dimensional Tolerances & Fit Control

Critical tolerances influencing installation:

Feature	Typical Tolerance
Shank diameter	h9
Square neck width	+0 / −0.1 mm
Head diameter	±0.3 mm
Thread pitch	ISO tolerance class
Straightness	≤0.2% of length

SM Fasteners maintains traceability through batch inspection and calibration records.

2.10 Geometry Influence on Load Performance

Square Neck Engagement

Torque resistance:$$T = F \times r$$

Where r equals half the square width.

Greater square width → improved anti-rotation capacity.

Head Bearing Area

$$A = \pi \times \left(\frac{d_k}{2}\right)^2$$

Larger heads reduce:

• Embedment
• Surface crushing
• Joint relaxation

2.11 Weight Chart — Carriage Bolts

(Typical carbon steel density basis — aligned with SM Fasteners manufacturing data)

Size	Length (mm)	Weight/Piece (kg)	Weight/100 pcs (kg)
M8	40	0.020	2.0
M10	50	0.038	3.8
M12	60	0.070	7.0
M16	80	0.165	16.5
M20	100	0.325	32.5
M24	120	0.580	58.0

Weight verification supports EPC logistics planning and export packing calculations.

2.12 Engineering Selection Logic

Engineers typically select carriage bolts using:

1. Load requirement
2. Joint material hardness
3. Corrosion environment
4. Installation accessibility
5. Applicable project standard
6. Inspection requirement

2.13 SM Fasteners Dimensional Manufacturing Capability

SM Fasteners supports:

• Metric & Imperial production
• Custom square neck dimensions
• Special head diameters
• Non-standard lengths
• PEEK carriage bolt engineering
• Project-specific tolerances

Production controlled under:

✔ ISO 9001 certified procedures
✔ UKAF-aligned inspection framework
✔ Full traceability and batch documentation

3. MATERIAL ENGINEERING, HEAT TREATMENT, MANUFACTURING WORKFLOW & SURFACE ENGINEERING

3.1 Materials Engineering Philosophy for Carriage Bolts

Material selection is the most critical engineering decision affecting:

• Load carrying capability
• Corrosion resistance
• Temperature performance
• Fatigue life
• Installation reliability
• Compliance with EPC project specifications

Carriage bolts operate frequently in mixed-material joints (timber, composites, structural steel, equipment frames). Therefore, materials must provide:

✔ Controlled hardness
✔ Adequate ductility for square neck embedding
✔ High clamp retention
✔ Environmental durability

SM Fasteners manufactures carriage bolts across a complete industrial alloy spectrum under ISO 9001 quality management systems.

3.2 Industrial Material Range

Standard Metallic Materials

Material Family	Common Grades	Characteristics	Typical Applications
Carbon Steel	ASTM A307, Grade 4.6–8.8	Economical, good strength	Construction & infrastructure
Alloy Steel	10.9, 12.9	High strength	Heavy equipment
Stainless Steel	A2-70, A4-80	Corrosion resistant	Marine & chemical
Duplex Stainless	2205	High strength + chloride resistance	Offshore
Super Duplex	2507	Extreme corrosion resistance	Oil & gas
Nickel Alloys	Monel 400	Seawater resistant	Marine hardware
Inconel	625 / 718	High temperature	Power & LNG
Incoloy	825	Acid resistance	Chemical plants
Hastelloy	C276	Aggressive chemicals	Refinery processing
SMO 254	6Mo stainless	Chloride resistance	Desalination
Nickel	Commercial Nickel	Chemical stability	Specialty equipment

Advanced Polymer Materials

PEEK Carriage Bolts

SM Fasteners manufactures precision PEEK (Polyether Ether Ketone) carriage bolts for specialized industries.

Property	Value
Continuous Service Temp	250°C
Chemical Resistance	Excellent
Electrical Insulation	Outstanding
Weight Reduction	~70% lighter than steel
Magnetic Neutrality	Yes

Applications

• Semiconductor manufacturing
• Chemical processing
• Offshore electrical isolation
• Hydrogen systems
• Medical equipment

3.3 Material Comparison Table

Material	UTS (MPa)	Yield (MPa)	Corrosion Resistance	Temperature Limit	Relative Cost	Typical Industry
Carbon Steel	400–800	240–640	Low	300°C	Low	Construction
Alloy Steel	900–1200	850+	Moderate	400°C	Medium	Heavy equipment
SS 304	700	450	Good	870°C	Medium	General industry
SS 316	800	550	Very Good	870°C	Medium-High	Marine
Duplex 2205	900	650	Excellent	300°C	High	Offshore
Super Duplex	1000	750	Extreme	300°C	Very High	Oil & gas
Monel 400	550	240	Seawater resistant	480°C	Very High	Marine
Inconel 625	1000	700	Extreme	980°C	Premium	LNG/Power
SMO 254	680	300	Chloride resistant	400°C	Premium	Desalination
PEEK	—	—	Chemical resistant	250°C	High	Electronics

3.4 Corrosion Resistance vs Environment

Environment	Carbon Steel	SS304	SS316	Duplex	Super Duplex	Nickel Alloys	PEEK
Indoor Industrial	✓	✓	✓	✓	✓	✓	✓
Marine Atmosphere	✗	△	✓	✓✓	✓✓	✓✓	✓
Seawater Immersion	✗	✗	△	✓	✓✓	✓✓	✓
Chloride Exposure	✗	△	✓	✓✓	✓✓	✓✓	✓
H₂S / Sour Service	✗	△	✓	✓✓	✓✓	✓✓	✓
Acidic Chemical	✗	△	✓	✓	✓✓	✓✓	✓✓
Cryogenic	✓	✓	✓	✓	✓	✓✓	✓
Electrical Isolation	✗	✗	✗	✗	✗	✗	✓✓

Legend: ✓✓ Excellent | ✓ Suitable | △ Limited | ✗ Not Recommended

Materials supplied by SM Fasteners can comply with NACE MR0175 / ISO 15156 where required.

3.5 Mechanical Property Requirements

Carriage bolts require balanced hardness to allow square neck deformation without fracture.

Mechanical Properties Table (ISO 898-1)

Property Class	Tensile Strength (MPa)	Yield Strength (MPa)	Hardness (HB)
4.6	400	240	120–220
5.8	500	400	150–240
8.8	800	640	220–300
10.9	1000	900	300–380

Excess hardness may cause neck cracking during installation.

3.6 Heat Treatment Processes

Heat treatment determines final mechanical performance.

3.6.1 Annealing

• Improves machinability
• Relieves forming stresses
• Used before cold heading

3.6.2 Quenching & Tempering

Primary strengthening process.

Steps:

1. Austenitizing
2. Rapid quenching
3. Tempering

Produces:

• High tensile strength
• Improved fatigue resistance

3.6.3 Normalizing

Refines grain structure for carbon steels.

3.6.4 Solution Annealing (Stainless Steel)

• Restores corrosion resistance
• Eliminates carbide precipitation

3.6.5 Hydrogen Embrittlement Relief Baking

Mandatory for plated high-strength bolts.

Typical condition:

• 200°C bake
• 2–24 hours depending on grade

SM Fasteners controls baking under ISO 9001 documented procedures.

3.7 Hardness Limits for Sour Service

Requirement	Value
NACE MR0175 Hardness Limit	≤22 HRC
Typical Grade Used	8.8 equivalent
Inspection Method	Rockwell C testing

Prevents sulfide stress cracking.

3.8 End-to-End Manufacturing Workflow

SM Fasteners follows a controlled manufacturing chain ensuring traceability and repeatability.

Step 1 — Raw Material Procurement

• Approved steel mills
• Heat number traceability
• EN 10204 3.1 Mill Test Certificate verification
• Chemical composition confirmation

Step 2 — Incoming Material Inspection

• Spectrometer PMI verification
• Diameter & surface checks
• Inclusion inspection

Step 3 — Cutting & Preparation

Wire rod cut into slugs.

Step 4 — Cold Heading / Hot Forging

Forms:

• Round head
• Square neck

Benefits:

• Grain flow continuity
• Higher fatigue resistance
• Minimal material waste

Step 5 — Trimming & Neck Calibration

Ensures precise anti-rotation geometry.

Step 6 — Thread Formation

Thread Rolling (Preferred)

Advantages:

• Increased fatigue strength
• Compressive surface stresses
• Smooth finish

Thread cutting used only for special alloys.

Step 7 — Heat Treatment

Controlled furnace cycles with batch recording.

Step 8 — Surface Preparation

• Shot blasting
• Pickling
• Cleaning

Step 9 — Surface Coating

Applied per customer specification.

Step 10 — Final Inspection & Traceability

• Dimensional verification
• Mechanical testing
• Batch marking
• Documentation release

3.9 Surface Engineering & Coatings

Surface treatments extend service life and reduce installation friction.

Surface Finish Comparison Table

Coating	Thickness	Corrosion Resistance	Friction	Typical Use
Plain Oil Finish	Minimal	Low	Medium	Indoor use
Zinc Electroplated	5–12 µm	Moderate	Low	General industry
Hot Dip Galvanized	40–80 µm	High	Higher torque	Structural
Mechanical Galvanized	15–30 µm	Good	Controlled	Transport
Zinc Flake (Geomet/Dacromet)	8–12 µm	Excellent	Stable	Automotive
PTFE Coated	Thin	Excellent	Very low	Chemical plants
Xylan	Thin	Excellent	Anti-galling	Offshore
Nickel Plating	Decorative/Corrosion	Moderate	Low	Equipment
Passivation (SS)	—	Restores corrosion resistance	Neutral	Stainless bolts

SM Fasteners validates coating thickness via calibrated gauges.

3.10 Coating Selection vs Environment

Environment	Recommended Finish
Indoor Machinery	Zinc plated
Outdoor Structures	HDG
Marine Offshore	SS316 / Duplex
Chemical Processing	PTFE/Xylan
Automotive	Zinc flake
High Temperature	Nickel alloy / Plain
Electrical Isolation	PEEK

3.11 Friction Control & Torque Stability

Surface finish directly affects preload accuracy.$$T = KFD$$

Where coating determines nut factor K.

Consistent coatings enable predictable torque–tension relationships required in EPC installations.

3.12 SM Fasteners Manufacturing Capability Integration

SM Fasteners supports:

• Custom alloy sourcing
• Project-specific heat treatment cycles
• NACE compliant materials
• PEEK precision machining
• Controlled coating partnerships
• Full traceability from raw material to dispatch

Manufacturing operates under:

✔ ISO 9001 Quality Management
✔ UKAF-aligned auditing practices
✔ MSME certified industrial production

4. INSPECTION, QUALITY CONTROL, APPLICATION ENGINEERING & GLOBAL EXPORT READINESS

4.1 Quality Philosophy — Carriage Bolt Manufacturing

Carriage bolts used in industrial assemblies must demonstrate:

• Dimensional conformity
• Verified mechanical performance
• Traceable metallurgy
• Consistent preload behavior
• Environmental durability

SM Fasteners integrates inspection and verification throughout production in accordance with ISO 9001 certified quality management systems, ensuring suitability for EPC, OEM, infrastructure, and energy-sector procurement.

4.2 Inspection & Quality Control Workflow

Quality assurance begins before manufacturing and continues through shipment release.

Inspection Stages

Stage	Inspection Activity	Objective
Raw Material	Chemical verification	Material conformity
Incoming Inspection	Diameter & surface checks	Defect elimination
In-Process	Forging geometry inspection	Neck accuracy
Thread Inspection	GO/NO-GO gauging	Fit control
Heat Treatment	Hardness verification	Mechanical compliance
Coating Inspection	Thickness measurement	Corrosion protection
Final Inspection	Dimensional + visual	Release approval
Pre-Dispatch	Documentation review	Traceability

4.3 Dimensional Inspection Requirements

Critical carriage bolt dimensions requiring verification:

Feature	Inspection Method
Head diameter	Digital caliper
Head height	Height gauge
Square neck width	Micrometer
Square neck height	Optical comparator
Shank diameter	Micrometer
Thread pitch	Thread gauge
Straightness	V-block inspection
Overall length	Caliper measurement

SM Fasteners maintains calibrated equipment traceable to international standards.

4.4 Mechanical Testing Requirements

Mandatory Mechanical Tests

Test	Standard	Purpose
Tensile Test	ISO 898-1	Strength verification
Proof Load Test	ISO 898	Elastic behavior
Hardness Test	ISO 6508	Heat treatment validation
Wedge Tensile Test	ISO	Head integrity
Impact Test (if required)	ASTM	Low-temperature service
Elongation Test	ISO	Ductility verification

4.5 Non-Destructive Testing (NDT)

Applied for critical industrial or offshore projects.

Method	Detection Capability
Magnetic Particle Inspection	Surface cracks
Dye Penetrant Testing	Fine surface defects
Ultrasonic Testing	Internal flaws
Eddy Current Testing	Material discontinuity
Visual Inspection	Surface defects

4.6 Positive Material Identification (PMI)

For alloy and corrosion-resistant materials.

Verification methods:

• XRF Spectrometry
• Optical Emission Spectroscopy

Ensures supplied material matches project specification.

4.7 Certification & Documentation

SM Fasteners supports full industrial documentation packages.

Standard Documentation Set

Document	Description
EN 10204 3.1 MTC	Chemical & mechanical certification
EN 10204 3.2	Third-party inspection
Heat Treatment Report	Furnace cycle records
Dimensional Inspection Report	Measurement verification
Coating Thickness Report	Corrosion protection validation
PMI Report	Alloy confirmation
Certificate of Conformity (CoC)	Compliance declaration
Packing List	Export logistics
Traceability Record	Batch identification

4.8 Tightening Torque Chart

(Typical values — Carbon Steel Property Class 8.8)

Size	Dry Torque (Nm)	Zinc Plated (Nm)	Lubricated (Nm)
M6	10	9	8
M8	25	22	20
M10	49	44	40
M12	85	80	70
M16	210	190	170
M20	410	370	330
M24	710	640	580

Actual torque values depend on lubrication and coating condition.

4.9 Preload Calculation — Engineering Table

Formula

$$F = \frac{T}{K \times D}$$

Where:

• F = Preload Force
• T = Torque
• K = Nut Factor
• D = Bolt Diameter

Example Calculation — M16 Carriage Bolt (Grade 8.8)

• Torque = 210 Nm
• Nut factor = 0.18
• Diameter = 0.016 m

$$F=\frac{210}{0.18\times0.016}$$

$$F=72,916\ N \approx 73\ kN$$

4.10 Thread Standards & Tolerances Table

Thread Type	Standard	Tolerance
Metric Coarse	ISO 261	6g
Metric Fine	ISO 965	6g
UNC	ASME B1.1	2A
UNF	ASME B1.1	2A
BSW	BS 84	Medium
BSF	BS 84	Close

4.11 Failure Prevention Through Inspection

Failure Mode	Inspection Control
Neck Spin-Out	Square dimension check
Fatigue Failure	Surface inspection
Hydrogen Embrittlement	Baking verification
Thread Galling	Surface finish control
Stress Corrosion	Material verification

4.12 Industry Application Mapping

Construction & Structural Steel

• Timber framing
• Guard rails
• Bridges
• Structural cladding

Oil & Gas Industry

Upstream

• Platform walkways
• Equipment guards

Midstream

• Pipeline supports
• Compressor stations

Downstream

• Refinery platforms
• Access systems

Duplex and nickel alloys selected where corrosion risk exists.

Power Generation

• Turbine housing guards
• Cable tray supports
• Cooling tower structures

Petrochemical & Chemical Processing

• Chemical tanks
• Pump bases
• Polymer plant equipment

PEEK carriage bolts used where electrical isolation is required.

LNG & Offshore

• Deck fittings
• Safety barriers
• Marine access structures

Materials:

• SS316
• Duplex
• Super Duplex
• Inconel

Automotive & Heavy Equipment

• Trailer bodies
• Agricultural machinery
• Conveyor systems

Railways & Infrastructure

• Signal structures
• Noise barriers
• Platform assemblies

Shipbuilding & Marine

• Deck equipment
• Interior fittings
• Composite structures

4.13 Weight Reference Chart (Engineering Logistics Table)

Size	Length	Weight/Piece (kg)	Weight/100 pcs (kg)
M8 × 40	0.020	2.0
M10 × 50	0.038	3.8
M12 × 60	0.070	7.0
M16 × 80	0.165	16.5
M20 × 100	0.325	32.5
M24 × 120	0.580	58.0

Aligned with SM Fasteners production data for export calculations.

4.14 Packaging & Preservation for Export

Industrial carriage bolts require protection against:

• Moisture
• Mechanical damage
• Thread contamination
• Corrosion during transit

Standard Packaging Methods

Method	Purpose
VCI Packaging	Corrosion prevention
Thread Protectors	Prevent damage
Heat-sealed bags	Moisture barrier
HDPE drums	Bulk shipment
Wooden crates	Heavy export orders

Export Compliance

• ISPM-15 fumigated wooden crates
• Container moisture control
• Barcode traceability labeling

4.15 Global Export Capability — SM Fasteners

SM Fasteners supports international project supply including:

• EPC contractors
• OEM manufacturers
• Global distributors
• Infrastructure megaprojects

Capabilities include:

✔ Metric & Imperial manufacturing
✔ Custom drawings production
✔ Exotic alloy sourcing
✔ PEEK precision fasteners
✔ Batch traceability systems
✔ Inspection witness support

4.16 Procurement Readiness for EPC Projects

Typical procurement submission includes:

• Technical datasheet
• GA dimensional drawing
• Material certificates
• Inspection test plan (ITP)
• Quality plan
• Packing specification
• Compliance statement

4.17 Integrated ISO 9001 Quality System

SM Fasteners applies ISO 9001 principles across:

• Supplier qualification
• Manufacturing control
• Calibration management
• Corrective action systems
• Continuous improvement
• Customer traceability support

UKAF-aligned auditing ensures international quality recognition.

4.18 Engineering Selection Summary

Carriage Bolt Selection Matrix

Requirement	Recommended Choice
Timber structure	Carbon steel HDG
Marine exposure	SS316 / Duplex
Chemical plant	PTFE coated / Nickel alloy
High strength	Property class 8.8
Electrical isolation	PEEK carriage bolt
Outdoor infrastructure	Hot dip galvanized

4.19 Engineering Advantages of SM Fasteners Carriage Bolts

• Precision square-neck forming
• Controlled thread rolling
• Verified heat treatment
• Advanced alloy capability
• Global standards compliance
• Export-ready packaging systems

All production aligned with:

ISO 9001 Certified Manufacturing
MSME Industrial Capability
UKAF Quality Framework