HEAVY HEX BOLT

1. Industry Context and Engineering Role

Heavy Hex Bolts are primary structural fastening elements designed for high-load, safety-critical bolted joints where superior clamping force, fatigue resistance, and installation reliability are mandatory.

Unlike standard hex bolts, heavy hex bolts incorporate:

• Larger head width across flats
• Increased bearing surface
• Higher torque capacity
• Improved load distribution

These characteristics make them the preferred fastening solution across:

Industry Sector	Functional Requirement
Structural Steel Construction	High preload structural joints
Oil & Gas	Pressure-containing flange assemblies
LNG & Offshore	Corrosion-resistant high-load connections
Power Plants	Turbine casings, boiler structures
Petrochemical	Thermal cycling resistant joints
Heavy Equipment	Dynamic load retention
Shipbuilding	Vibration and fatigue resistance
Infrastructure	Bridges, rail systems

SM Fasteners manufactures heavy hex bolts engineered for global EPC project compliance, ensuring compatibility with ASTM, ISO, DIN, and BS systems.

2. Technical Definition

A Heavy Hex Bolt is defined as:

A threaded fastener featuring a hexagonal head with dimensions larger than standard hex bolts, intended for structural and high-pressure bolted connections requiring elevated preload and enhanced load distribution.

Key Characteristics

• Hexagonal external drive
• Partial or full threading
• Controlled mechanical properties
• Tight dimensional tolerances
• Designed for nut-based assemblies

3. Functional Role in Bolted Assemblies

Heavy hex bolts create clamped joints, not shear pins.

The bolt’s primary purpose is:

✅ Generate preload
✅ Maintain compression between components
✅ Prevent joint separation
✅ Transfer external loads through friction

Bolt Joint Load Transfer Principle

When tightened:

1. Bolt elongates elastically.
2. Joint members compress.
3. Clamp force resists service loads.

4. Load Mechanics & Force Behavior

4.1 Axial Tensile Loading

The dominant working condition.$$F = \frac{T}{K \times D}$$

Where:

• F = preload force
• T = tightening torque
• K = nut factor
• D = nominal diameter

4.2 Shear Loading

Heavy hex bolts should not rely solely on shear strength.

Preferred design:

• Friction-type joint
• Preload carries shear through interface friction.

4.3 Combined Loading

Typical industrial joints experience:

• Axial tension
• Transverse shear
• Bending stress
• Thermal expansion forces

Heavy hex geometry improves stability under combined stresses.

5. Preload and Clamping Force Principles

Correct preload is essential because:

• Too low → joint loosening
• Too high → yielding or fracture

Recommended preload:$$70\% – 75\% \text{ of Proof Load}$$

Example — Preload Calculation

Bolt: M24 Property Class 10.9
Proof Load ≈ 830 MPa

Stress area:$$A_s = 353 \ mm^2$$

Proof force:$$F_p = 830 \times 353 = 293\,000 \ N$$

Recommended preload:$$F = 0.7 \times 293 = 205 \ kN$$

6. Torque–Tension Relationship

Torque does not directly equal preload.

Approximate energy distribution:

Energy Component	Percentage
Thread friction	40–45%
Bearing friction	45–50%
Useful preload	10–15%

Therefore lubrication, coatings, and surface finish strongly influence performance.

Typical Nut Factor Values

Condition	Nut Factor (K)
Dry carbon steel	0.20–0.24
Zinc plated	0.18–0.22
Lubricated	0.14–0.18
PTFE coated	0.10–0.13

SM Fasteners supplies controlled-coefficient coated fasteners to stabilize torque accuracy.

7. Joint Design Principles

7.1 Grip Length Optimization

Ideal:$$Grip Length ≥ 3D$$

Ensures elastic energy storage and fatigue resistance.

7.2 Thread Engagement

Minimum engagement:

Material	Engagement
Steel	1 × diameter
Cast iron	1.5 × diameter
Aluminum	2 × diameter

7.3 Bearing Surface Importance

Heavy hex head increases:

• Contact area
• Reduced embedment relaxation
• Better gasket compression

Critical for flange assemblies.

8. Friction and Interface Behavior

Joint reliability depends on:

• Surface roughness
• Coating friction coefficient
• Washer hardness
• Lubrication control

SM Fasteners supports engineered friction solutions aligned with ISO 16047 torque testing principles.

9. Failure Mechanisms in Heavy Hex Bolts

9.1 Fatigue Failure

Cause:

• Cyclic load variation
• Insufficient preload

Prevention:

• High preload ratio
• Rolled threads
• Smooth fillet radius

9.2 Shear Failure

Occurs when:

• Joint slips
• Bolt carries transverse load directly

Design solution:

• High clamp force friction joints.

9.3 Hydrogen Embrittlement

Risk in high-strength bolts (>1000 MPa).

Controls at SM Fasteners:

• Baking after plating
• Controlled electroplating
• ASTM F1941 compliance

9.4 Stress Corrosion Cracking

Critical environments:

• H₂S sour service
• Chloride exposure
• High temperature pressure systems

Material selection must follow:

NACE MR0175 / ISO 15156

9.5 Embedment Relaxation

Surface flattening reduces preload.

Heavy hex heads reduce this effect due to larger bearing area.

10. Heavy Hex Bolts vs Standard Hex Bolt

Feature	Heavy Hex	Standard Hex
Head size	Larger	Smaller
Load capacity	Higher
Structural use	Preferred
Flange applications	Standard
Torque capability	Higher
EPC specification usage	Very High

11. Engineering Selection Criteria

Engineers must evaluate:

• Design load
• Temperature exposure
• Corrosion environment
• Installation method
• Maintenance access
• Inspection requirement
• Certification needs

SM Fasteners provides engineering support for custom specification alignment across global projects.

12. Product Types and Variants

Heavy Hex Bolts are produced in multiple configurations to satisfy structural engineering, pressure equipment, and industrial mechanical assembly requirements.

Selection depends on:

• Load classification
• Installation access
• Joint configuration
• Environmental exposure
• Inspection requirements

SM Fasteners manufactures both standardized and custom-engineered heavy hex bolts aligned with international EPC specifications.

12.1 Fully Threaded Heavy Hex Bolts

Description

Threads extend across the entire shank length.

Engineering Advantages

• Maximum thread engagement
• Suitable for variable grip lengths
• High adaptability for maintenance operations

Applications

• Equipment mounting
• Machinery frames
• Maintenance replacement assemblies

12.2 Partially Threaded Heavy Hex Bolts

Description

Unthreaded shank (grip section) between head and threads.

Engineering Advantages

• Higher fatigue resistance
• Improved shear capacity
• Reduced stress concentration

Applications

• Structural steel joints
• Flanged pressure vessels
• Bridge construction

12.3 Heavy Hex Structural Bolts

Commonly manufactured to:

• ASTM A325
• ASTM A490
• EN 14399

Characteristics:

• Controlled mechanical properties
• Designed for pretensioned structural joints
• Used with hardened washers and nuts.

12.4 Heavy Hex Bolts for Pressure Flanges

Standards:

• ASTM A193
• ASTM A320

Typical service:

• High temperature
• Cryogenic service
• Pressure-containing systems

12.5 High Temperature Alloy Heavy Hex Bolts

Materials:

• Inconel
• Incoloy
• Hastelloy
• SMO 254
• Duplex & Super Duplex Stainless Steel

Used where:

• Thermal creep resistance required
• Corrosion resistance critical

12.6 PEEK Heavy Hex Bolts (Specialized Applications)

SM Fasteners manufactures engineered PEEK fasteners for:

• Electrical insulation assemblies
• Semiconductor equipment
• Chemical processing environments

Advantages:

• Non-metallic
• Lightweight
• Excellent chemical resistance
• Temperature capability up to ~250°C

13. Dimensional Logic and Geometry Engineering

Heavy hex bolt geometry directly affects:

• Torque transmission
• Bearing stress
• Installation reliability
• Structural performance

13.1 Heavy Hex Head Geometry

Key dimensional parameters:

Parameter	Symbol	Function
Nominal diameter	D	Load capacity
Thread pitch	P	Engagement strength
Width across flats	S	Wrenching torque
Head height	K	Strength under torque
Thread length	b	Engagement control
Under-head radius	r	Fatigue resistance

Heavy hex heads are approximately 1.5× standard hex head bearing area.

14. Dimensional Specification Table (Metric Heavy Hex Bolt )

(Typical reference aligned with ISO/DIN practice — SM Fasteners supplies custom dimensions as required.)

Size	Pitch (mm)	Head Width S (mm)	Head Height K (mm)	Thread Length b (mm)
M12	1.75	21	8	30
M16	2.0	27	10	38
M20	2.5	34	13	46
M24	3.0	41	15	54
M27	3.0	46	17	60
M30	3.5	50	19	66
M36	4.0	60	23	78
M42	4.5	70	26	90
M48	5.0	75	30	102

Dimensions verified through calibrated inspection systems under ISO 9001 quality management at SM Fasteners.

15. Inch Series Heavy Hex Bolt Dimensions (ASTM Practice)

Size	Threads	Head Width (in)	Head Height (in)
1/2″	UNC	7/8	11/32
3/4″	UNC	1-1/4	1/2
1″	UNC	1-5/8	5/8
1-1/4″	UNC	2	3/4
1-1/2″	UNC	2-3/8	7/8
2″	UNC	3	1-1/8

16. Thread Systems & Engineering Logic

Thread form selection affects:

• Load capacity
• Assembly speed
• Fatigue resistance
• Galling tendency

Thread Standards & Tolerances

System	Standard	Thread Angle	Typical Tolerance
Metric	ISO 261 / ISO 965	60°	6g / 6H
UNC	ASME B1.1	60°	2A / 2B
UNF	ASME B1.1	60°	2A / 2B
BSW	BS 84	55°	Medium
BSF	BS 84	55°	Fine
NPT (special)	ASME B1.20	60°	Taper

SM Fasteners manufactures threads through controlled rolling processes ensuring superior fatigue performance.

17. Thread Pitch Selection Logic

Condition	Recommended Pitch
Structural joints	Coarse
High vibration	Fine
Limited engagement	Fine
Rapid assembly	Coarse
Soft materials	Coarse

18. Applicable International Standards

Heavy Hex Bolts must comply with recognized engineering standards to ensure interchangeability and safety.

ASTM Standards

Standard	Application
ASTM A325	Structural bolts
ASTM A490	High strength structural
ASTM A193	High temperature pressure service
ASTM A320	Low temperature service
ASTM F3125	Structural bolt specification
ASTM F568M	Metric mechanical properties

ISO Standards

Standard	Scope
ISO 4014	Hex bolts partial thread
ISO 4017	Fully threaded bolts
ISO 898-1	Mechanical properties
ISO 965	Thread tolerance
ISO 3269	Acceptance inspection

DIN Standards

Standard	Description
DIN 6914	Heavy hex structural bolt
DIN 933	Full thread
DIN 931	Partial thread

British Standards (BS)

Standard	Description
BS 3692	Metric bolts
BS EN 14399	Structural preloaded bolts
BS 4190	Inch bolts

19. Property Class Systems

Mechanical classification ensures predictable strength.

Metric Property Classes

Class	Tensile Strength (MPa)	Yield Ratio
8.8	800	0.8
10.9	1040	0.9
12.9	1220	0.9

ASTM Structural Grades

Grade	Minimum Tensile Strength
A325	~830 MPa
A490	~1040 MPa

20. Interchangeability Considerations

Critical procurement rule:

Heavy hex bolts are not always interchangeable across standards.

Factors affecting interchangeability:

• Head dimensions
• Thread tolerance class
• Proof load differences
• Washer compatibility
• Nut height requirements

SM Fasteners supports cross-standard equivalency verification during EPC procurement to avoid installation mismatch.

21. Engineering Fit Between Bolt–Nut–Washer

Correct system includes:

• Heavy hex bolt
• Compatible heavy hex nut
• Hardened washer

This ensures:

• Proper preload transfer
• Prevention of embedding
• Accurate torque application

22. Dimensional Inspection Requirements

Typical inspection sequence:

1. Major diameter measurement
2. Pitch verification
3. Thread ring gauge inspection
4. Head dimension check
5. Straightness inspection
6. Surface integrity evaluation

All inspections performed under calibrated equipment traceable to international standards within SM Fasteners’ ISO 9001 system.

23. Geometry Influence on Mechanical Performance

Geometry Feature	Performance Impact
Larger head	Reduced bearing stress
Rolled threads	Improved fatigue life
Fillet radius	Crack resistance
Controlled pitch	Accurate preload
Proper grip length	Elastic energy storage

24. Material Grades and Engineering Selection Criteria

Material selection for heavy hex bolts determines:

• Mechanical strength
• Corrosion resistance
• Temperature capability
• Fatigue life
• Sour-service compliance
• Lifecycle cost

SM Fasteners manufactures heavy hex bolts across full industrial alloy ranges, enabling EPC buyers and engineers to match material performance precisely with operating environments.

25. Industrial Material Categories

25.1 Carbon Steel Heavy Hex Bolts

Typical Standards:

• ASTM A307
• ASTM A325
• ISO Property Class 8.8

Characteristics

• High structural strength
• Economical solution
• Suitable for atmospheric exposure

Typical Applications

• Structural steel
• Infrastructure
• Equipment foundations

25.2 Alloy Steel Heavy Hex Bolts

Standards:

• ASTM A490
• ASTM A193 B7 / B16
• Property Class 10.9 / 12.9

Advantages

• High tensile strength
• Excellent fatigue resistance
• Elevated temperature capability

Used in:

• Oil & Gas flanges
• Power plant systems
• High-pressure equipment

25.3 Stainless Steel Heavy Hex Bolts

Common Grades:

• SS304 / A2-70
• SS316 / A4-80
• 316L
• 904L

Benefits:

• Corrosion resistance
• Hygienic suitability
• Excellent atmospheric durability

Applications:

• Chemical plants
• Marine installations
• Water treatment facilities

25.4 Duplex & Super Duplex Stainless Steel

Grades:

• UNS S31803
• UNS S32205
• UNS S32750
• UNS S32760

Advantages:

• High strength + corrosion resistance
• Excellent chloride resistance
• Offshore suitability

Compliant with NACE MR0175 / ISO 15156.

25.5 Nickel & High-Performance Alloys

SM Fasteners supplies advanced materials including:

• Inconel 625 / 718
• Incoloy 800 / 825
• Hastelloy C276
• Monel 400
• SMO 254

Used for:

• LNG facilities
• Acid processing
• High-temperature reactors
• Seawater systems

25.6 PEEK Heavy Hex Bolts (Advanced Engineering Polymers)

Applications requiring:

• Electrical insulation
• Magnetic neutrality
• Chemical inertness

Properties:

• Continuous temperature ≈ 250°C
• Excellent chemical resistance
• Lightweight non-metallic solution

26. Material Comparison Table

| Material | UTS (MPa) | Yield (MPa) | Corrosion Resistance | Temp Limit | Relative Cost | Typical Use |
|—|—|—|—|—|—|
| Carbon Steel | 400–800 | 250–640 | Low | 300°C | Low | Structural |
| Alloy Steel | 830–1200 | 700–1100 | Moderate | 450°C | Medium | Pressure service |
| SS304 | 700 | 450 | Good | 425°C | Medium | General industry |
| SS316 | 800 | 550 | Very Good | 450°C | Medium | Marine/chemical |
| Duplex | 800–950 | 550–750 | Excellent | 300°C | High | Offshore |
| Super Duplex | 950+ | 750+ | Extreme | 300°C | Very High | Seawater |
| Inconel | 1000+ | 700+ | Extreme | 700°C | Premium | High temp |
| SMO 254 | 650 | 300 | Extreme | 300°C | Premium | Chloride service |
| PEEK | — | — | Excellent | 250°C | High | Electrical/chemical |

27. Corrosion Resistance vs Environment

Environment	Recommended Material
Marine / Seawater	Duplex / Super Duplex / SMO 254
Sour Gas (H₂S)	A193 B7M / Duplex
Acidic Chemical	Hastelloy / Incoloy
High Temperature	B16 / Inconel
Cryogenic LNG	A320 L7 / Stainless
Outdoor Infrastructure	Galvanized Carbon Steel
Chemical Insulation	PEEK Fasteners

28. Mechanical Properties — Grade Wise

Property Class	Tensile Strength MPa	Yield MPa	Hardness (HV)
8.8	≥800	≥640	250–320
10.9	≥1040	≥940	320–380
12.9	≥1220	≥1100	380–435

SM Fasteners controls hardness ranges to prevent hydrogen embrittlement risks.

29. Heat Treatment Processes

Heat treatment is essential to achieve required mechanical performance.

29.1 Quenching and Tempering

Used for:

• Alloy steel bolts
• Property class 8.8–12.9

Process:

1. Austenitizing
2. Rapid quenching
3. Tempering

Benefits:

• High strength
• Toughness balance
• Controlled hardness

29.2 Normalizing

Improves:

• Grain refinement
• Machinability
• Structural uniformity

29.3 Solution Annealing (Stainless Steel)

Purpose:

• Dissolve carbides
• Restore corrosion resistance
• Improve ductility

29.4 Stress Relieving

Applied after machining or rolling to reduce residual stresses.

29.5 Sour Service Hardness Control

Per NACE MR0175:

• Maximum hardness limits enforced
• Prevent sulfide stress cracking

30. End-to-End Manufacturing Workflow

(SM Fasteners Production Methodology)

Step 1 — Raw Material Procurement

• Approved steel mills only
• Heat number traceability
• Mill Test Certificate verification

Step 2 — Incoming Material Inspection

Verification includes:

• Chemical analysis
• Ultrasonic testing
• PMI verification
• Dimensional confirmation

Step 3 — Cutting & Preparation

• Automatic bar cutting
• Weight control
• Surface defect inspection

Step 4 — Hot Forging / Cold Heading

Heavy hex bolts typically hot forged for:

• Grain flow alignment
• Superior fatigue resistance
• Structural strength

Step 5 — Trimming & Head Formation

Ensures:

• Accurate head geometry
• Consistent wrench fit
• Reduced stress concentration

Step 6 — Thread Formation

Thread Rolling (Preferred)

Advantages:

• Increased fatigue life
• Compressive surface stress
• Improved thread strength

Thread cutting used only for specialty alloys or large diameters.

Step 7 — Heat Treatment

Conducted in controlled furnaces with:

• Temperature recording
• Controlled cooling
• Batch traceability

Step 8 — Straightening & Cleaning

• Shot blasting
• Scale removal
• Surface preparation for coating

Step 9 — Surface Finishing / Coating

(See Section 31)

Step 10 — Final Inspection & Identification

• Marking per ASTM/ISO
• Lot traceability
• QA release

31. Surface Finishing & Coating Engineering

Coating selection affects:

• Corrosion resistance
• Friction coefficient
• Torque accuracy
• Service life

Surface Finish Comparison Table

Finish	Corrosion Resistance	Friction Control	Temperature Limit	Application
Black Oxide	Low	Stable	300°C	Indoor
Zinc Plated	Moderate	Good	120°C	General
HDG	High	Variable	200°C	Structural
Mechanical Galv.	High	Controlled	200°C	Structural
PTFE/Xylan	Excellent	Low friction	260°C	Offshore
Cadmium (special)	High	Excellent	Aerospace	Controlled use
Nickel Plating	High	Good	400°C	Chemical
Dacromet/Geomet	Very High	Controlled	300°C	Automotive
Passivation	Improves SS	Neutral	High	Stainless steel

SM Fasteners provides engineered coating selection matched to project specifications.

32. Hydrogen Embrittlement Prevention

Critical for grades ≥10.9.

Controls implemented:

• Low hydrogen plating processes
• Post-plating baking
• Hardness verification
• Process validation

33. Coating Selection vs Environment

Environment	Recommended Finish
Offshore	PTFE / Xylan
Structural Outdoor	Hot Dip Galvanized
Chemical Plant	Nickel / Stainless
High Temperature	Black oxide / Alloy steel
Electrical Systems	PEEK Fasteners

34. Manufacturing Traceability System

Each SM Fasteners heavy hex bolt can be traced via:

• Heat number
• Batch number
• Material grade marking
• Inspection record linkage

Integrated under ISO 9001 quality management framework.

35. Inspection & Quality Control Philosophy

Heavy Hex Bolts are frequently used in safety-critical assemblies where failure consequences include:

• Structural collapse
• Pressure leakage
• Equipment shutdown
• Environmental hazards

Therefore, SM Fasteners integrates multi-stage quality assurance aligned with:

• ISO 9001 Quality Management System
• ISO 3269 Fastener Acceptance Inspection
• ASTM Mechanical Testing Standards
• EPC Third-Party Inspection Requirements

36. Dimensional Inspection Procedures

Incoming & In-Process Verification

Inspection Item	Method	Standard
Major diameter	Micrometer	ISO 965
Pitch verification	Thread gauge	ISO / ASME
Head dimensions	Vernier/CMM	ISO 4014
Thread fit	GO/NO-GO gauges	ASME B1.2
Straightness	Dial indicator	ISO 4759
Under-head radius	Optical inspection	DIN 6914

Calibration traceability maintained through UKAF-recognized systems.

37. Mechanical Testing Requirements

Test	Purpose	Standard
Tensile Test	Verify strength	ISO 898-1
Proof Load Test	Elastic limit	ASTM F606
Hardness Test	Heat treatment control	ISO 6508
Wedge Tensile	Head integrity	ASTM F606
Impact Test	Low temp toughness	ASTM A370
Elongation	Ductility	ISO 6892

38. Non-Destructive Testing (NDT)

Applied based on project criticality.

NDT Method	Detects
Magnetic Particle Testing	Surface cracks
Ultrasonic Testing	Internal defects
Dye Penetrant	Surface discontinuities
PMI Testing	Alloy verification
Eddy Current	Surface flaws

39. Positive Material Identification (PMI)

Mandatory for:

• Duplex
• Super Duplex
• Nickel Alloys
• Sour Service Bolting

Verification ensures chemical compliance with project material specifications.

40. Certification & Documentation

SM Fasteners provides complete documentation packages required by EPC projects.

Standard Deliverables

• EN 10204 3.1 Material Test Certificate
• Heat Treatment Reports
• Dimensional Inspection Reports
• Mechanical Test Reports
• Coating Thickness Report
• Hardness Verification
• Certificate of Conformance (CoC)

Optional

• EN 10204 3.2 Third-Party Certification
• NACE Compliance Statement
• IBR Documentation (India)
• Project Data Books

41. Industrial Application Mapping

Construction & Structural Steel

Used for:

• High-strength friction grip joints
• Bridges
• Towers
• Steel frameworks

Preferred grades:
A325, A490, 8.8, 10.9

Oil & Gas Industry

Upstream

• Wellhead equipment
• Drilling structures

Midstream

• Pipeline flanges
• Compressor stations

Downstream

• Refineries
• Process reactors

Materials:
A193 B7, B16, Duplex, Inconel.

Power Generation

Applications:

• Turbine casing bolting
• Boiler assemblies
• Generator housings

High temperature alloy steels required.

Petrochemical & Chemical Processing

Requirements:

• Corrosion resistance
• Chemical compatibility
• Thermal stability

Materials:
316L, SMO 254, Hastelloy.

LNG & Cryogenic Systems

Low temperature resistance required.

Typical grades:
ASTM A320 L7/L43.

Offshore & Marine

Challenges:

• Chloride attack
• Fatigue loading
• Salt spray

Preferred:
Super Duplex, PTFE coated bolts.

Automotive & Heavy Equipment

Uses:

• Chassis assemblies
• Earthmoving equipment
• Mining machinery

Property classes 10.9–12.9 dominate.

Railways & Infrastructure

Applications:

• Track structures
• Bridge assemblies
• Signaling systems

Hot dip galvanized heavy hex bolts widely used.

Shipbuilding

Applications:

• Engine mounting
• Deck structures
• Hull assemblies

Materials:
Duplex and stainless steel.

PEEK Fastener Applications

Where metal fasteners are unsuitable:

• Electrical insulation panels
• Semiconductor equipment
• MRI and electronic assemblies
• Chemical reactors

42. Failure Prevention Through Engineering Controls

Failure Mode	Prevention Strategy
Fatigue cracking	Proper preload
Galling	Lubricated coating
SCC	Correct alloy selection
Hydrogen embrittlement	Baking + hardness control
Joint loosening	Torque control + washers

MANDATORY ENGINEERING TABLES

43. Proof Load & Tensile Strength Table

Grade	Proof Load (MPa)	Tensile Strength (MPa)
8.8	600	800
10.9	830	1040
12.9	970	1220
A325	660	830
A490	830	1040

44. Tightening Torque Chart

(Lubricated condition, approximate engineering values)

Size	8.8 Torque (Nm)	10.9 Torque (Nm)	12.9 Torque (Nm)
M12	85	120	140
M16	210	300	350
M20	410	580	680
M24	710	1000	1170
M30	1420	2000	2350
M36	2450	3450	4000

Torque values depend on friction coefficient and coating condition.

45. Preload Calculation Formula (Engineering Reference)

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

Where:

• F = Preload (N)
• T = Applied Torque (Nm)
• K = Nut Factor
• D = Nominal Diameter (m)

Worked Example

M24 bolt
Torque = 1000 Nm
K = 0.18$$F = \frac{1000}{0.18 \times 0.024}$$F=0.18×0.0241000​ $$F = 231,000 \ N \approx 231 kN$$F=231,000 N≈231kN

46. Thread Standards & Tolerance Table

System	Tolerance Class	Fit
Metric	6g / 6H	General
Metric Precision	4g6g	High accuracy
UNC	2A / 2B	Standard
UNF	3A / 3B	Precision
BSW	Medium	Legacy
BSF	Fine	High vibration

47. Surface Finish Performance Comparison

Coating	Salt Spray Resistance	Friction Stability	Maintenance Need
Zinc	72–120 hrs	Moderate	Medium
HDG	500+ hrs	Variable	Low
PTFE	1000+ hrs	Excellent	Very Low
Nickel	600+ hrs	Stable	Low
Black Oxide	Minimal	Good	High

48. Corrosion Resistance vs Environment Table

Environment	Recommended Material / Finish
Offshore	Super Duplex + PTFE
Acidic Plant	Hastelloy
Marine	316 / Duplex
Structural Outdoor	HDG Carbon Steel
High Temp Furnace	Alloy Steel B16
Chemical Insulation	PEEK

49. Weight Chart — Heavy Hex Bolts

(Typical reference aligned with SM Fasteners production data)

Size	Weight / Piece (kg)	Weight / 100 pcs (kg)
M12 × 50	0.07	7
M16 × 60	0.14	14
M20 × 80	0.30	30
M24 × 100	0.56	56
M30 × 120	1.05	105
M36 × 150	2.05	205
M42 × 180	3.45	345
M48 × 200	5.10	510

Weight control verified during manufacturing for logistics accuracy.

50. Industrial Packaging & Export Readiness

SM Fasteners supplies heavy hex bolts prepared for international shipment.

Industrial Packaging

• VCI anti-corrosion packing
• Thread protection caps
• Oil preservation coating
• Moisture barrier wrapping

Export Packaging

• Heat-treated wooden crates
• ISPM-15 compliant pallets
• Container optimization
• Batch segregation

51. Global Supply & Documentation Capability

SM Fasteners supports EPC procurement cycles through:

• Custom engineering production
• Multi-material manufacturing capability
• Project batch traceability
• Inspection coordination with TPI agencies
• Global export logistics readiness

Deliverables include:

• MTC
• Heat treatment charts
• Inspection dossiers
• Compliance certification
• Packing lists & traceability matrices

52. SM Fasteners Engineering Capability Summary

SM Fasteners operates as a precision fastener manufacturer delivering:

✔ ISO 9001 certified quality systems
✔ MSME registered industrial manufacturing
✔ UKAF accredited inspection compliance
✔ Advanced alloy manufacturing capability
✔ PEEK engineered fastener solutions
✔ Custom heavy hex bolt engineering
✔ Global EPC project supply readiness