Cap Nut Protective

1. Industry Context

Cap Nuts — commonly known as Protective Cap Nuts, Dome Nuts, Acorn Nuts, or Closed-End Nuts — represent a specialized fastening solution designed to combine mechanical retention with thread protection, sealing enhancement, and personnel safety.

Within industrial assemblies supplied to:

• Oil & Gas EPC Projects
• Structural Steel Fabrication
• Power Generation Systems
• Petrochemical Equipment
• Offshore & Marine Installations
• Heavy Machinery Manufacturing

cap nuts are not decorative components; they function as protective mechanical elements that enhance durability and lifecycle reliability.

Unlike standard hex nuts, a cap nut incorporates a fully enclosed dome which prevents exposure of threaded bolt ends to:

• Atmospheric corrosion
• Mechanical damage
• Contaminant ingress
• Human contact hazards

In high-reliability engineering environments, exposed threads frequently become failure initiation points. Protective cap nuts mitigate these risks.

SM Fasteners manufactures cap nuts under controlled ISO 9001 quality systems with material traceability suitable for global EPC procurement.

2. Technical Definition

A Cap Nut (Protective) is defined as:

A threaded fastening element with a closed or domed end designed to completely cover the protruding male thread while providing standard nut clamping functionality.

Core Functional Characteristics

Function	Engineering Purpose
Thread Protection	Prevents corrosion and galling
Safety	Eliminates exposed sharp threads
Environmental Shielding	Reduces moisture/chemical ingress
Aesthetic Finish	Required in visible assemblies
Assembly Reliability	Maintains thread integrity during service

Geometry Overview

Key geometric features:

• Hexagonal driving face
• Internal threaded bore
• Closed dome cavity
• Bearing face
• Optional sealing interface

Two main dome styles:

1. Low Crown Cap Nut
2. High Dome Cap Nut

The dome height determines allowable bolt projection.

3. Functional Role in Mechanical Assemblies

Cap nuts perform dual engineering roles:

3.1 Primary Function — Load Bearing Fastener

The nut creates clamping force identical to a standard hex nut.

Load transfer occurs through:

• Thread flank contact
• Bearing face compression
• Bolt tension generation

3.2 Secondary Function — Protective Barrier

The enclosed cavity:

• Prevents electrolyte formation
• Avoids thread oxidation
• Reduces hydrogen ingress risk
• Protects coatings on bolt threads

This is critical in:

• Offshore platforms
• Chemical plants
• Food processing equipment
• Public infrastructure assemblies

4. Load Mechanics & Force Behavior

4.1 Preload Generation

When torque is applied:$$F_p = \frac{T}{K \times D}$$

Where:

• $F_p$​ = Bolt preload force (N)
• $T$ = Applied torque (Nm)
• $K$ = Nut factor (friction coefficient)
• $D$ = Nominal diameter (m)

Approximately 85–90% of torque is consumed overcoming friction.

Only 10–15% produces useful preload.

4.2 Force Distribution in Cap Nuts

Compared with open nuts:

Parameter	Standard Hex Nut	Cap Nut
Load Path	Open	Closed dome constraint
Bolt Projection	Allowed	Limited
Thread Exposure	Yes	None
Corrosion Initiation	Higher	Reduced

The dome does not carry structural load — it functions purely as protection.

4.3 Stress Behavior

Major stresses include:

• Axial tensile stress
• Thread shear stress
• Bearing compression stress
• Residual stress from tightening

Failure occurs if bolt projection contacts dome top prematurely.

Engineering Rule:
Bolt engagement depth must be less than dome internal height.

5. Joint Design Principles

5.1 Thread Engagement Requirement

Minimum engagement:$$L_e \geq 1.0 \times D$$

For softer materials:$$L_e = 1.5D$$

5.2 Dome Clearance Requirement

Required internal clearance:

Bolt Size	Minimum Clearance
M6–M10	1.5–2 mm
M12–M20	2–4 mm
M24+	4–6 mm

Incorrect clearance leads to:

• False torque readings
• Under-preloaded joints
• Fatigue loosening

5.3 Torque–Tension Relationship

Critical variables:

• Surface coating
• Lubrication
• Thread tolerance
• Material hardness pairing

Cap nuts often exhibit slightly higher friction factors due to enclosed air compression and increased thread contact area.

6. Clamping Force Mechanics

Typical preload distribution:

Torque Energy Use	Percentage
Thread friction	40–50%
Bearing friction	35–45%
Useful preload	10–15%

Proper lubrication dramatically improves preload accuracy.

7. Failure Mechanisms

7.1 Fatigue Failure

Caused by insufficient preload.

Common in

7.2 Thread Stripping

Occurs when:$$\tau_{thread} > \tau_{material}$$

Typically seen in low-strength stainless assemblies.

7.3 Hydrogen Embrittlement

Risk conditions:

• High strength carbon/alloy steels
• Electroplated coatings
• Offshore hydrogen exposure

SM Fasteners controls hardness limits to prevent embrittlement.

7.4 Stress Corrosion Cracking (SCC)

Observed in:

• Chloride environments
• High temperature chemical plants

Materials like Duplex SS and SMO 254 are selected accordingly.

8. Engineering Selection Criteria

Cap nut selection depends on:

Parameter	Consideration
Mechanical load	Property class requirement
Environment	Corrosion resistance
Bolt projection	Dome depth
Inspection requirement	Closed-end suitability
Temperature	Material stability

9. Application Relevance in Assemblies

Cap nuts are preferred where:

• Personnel safety regulations exist
• Hygienic surfaces required
• Visual inspection important
• Thread contamination unacceptable

Typical assemblies:

• Handrails
• Rotating equipment guards
• Valve stems
• Food processing conveyors
• Marine deck fittings

10. SM FASTENERS Engineering Positioning

Under ISO 9001 and UKAF accreditation, SM Fasteners integrates:

• Controlled forging processes
• Advanced alloy material capability
• Custom dome depth engineering
• Precision thread manufacturing
• Export-grade inspection traceability

Manufacturing scope includes:

• Stainless steels
• Duplex & Super Duplex
• Nickel alloys
• PEEK protective cap nuts for non-metallic assemblies

11. Product Types and Variants of Cap Nuts (Protective)

Cap nuts are engineered in multiple configurations to satisfy mechanical loading conditions, environmental exposure requirements, and assembly constraints encountered in EPC and OEM applications.

SM Fasteners manufactures cap nuts according to international dimensional systems while supporting custom engineered variants.

11.1 Standard Dome (Acorn) Cap Nut

Description:
Fully closed hemispherical dome covering the entire bolt projection.

Engineering Characteristics

• Standard hex driving face
• Full thread engagement
• Maximum corrosion protection
• Improved personnel safety

Typical Applications

• Structural handrails
• Machinery guards
• Architectural steel
• Public infrastructure

11.2 High Crown Cap Nut

Designed with increased internal cavity depth.

Advantages

• Accommodates longer bolt projection
• Enables tolerance compensation
• Suitable for heavy structural assemblies

Used In

• Heavy equipment frames
• Power plant structures
• Offshore installations

11.3 Low Crown Cap Nut

Reduced dome height.

Engineering Purpose

• Compact installations
• Limited clearance zones
• Weight-sensitive assemblies

Common in automotive and equipment enclosures.

11.4 Stainless Hygienic Cap Nut

Special surface profile minimizing contamination retention.

Typical sectors:

• Food processing
• Pharmaceutical plants
• Cleanroom equipment

Often supplied in A2 / A4 stainless steel with polished finish.

11.5 Sealing Cap Nut (Protective Variant)

Incorporates:

• Nylon insert
• O-ring seal
• PTFE sealing washer

Provides:

• Splash protection
• Moisture ingress resistance
• Vibration resistance

Used in marine and outdoor electrical assemblies.

11.6 heavy hex nut /Cap Nut

Oversized hex profile for high preload applications.

Benefits:

• Larger bearing surface
• Improved load distribution
• Higher torque capacity

Used in:

• Petrochemical flanges
• Pressure equipment
• Structural bolting systems

11.7 PEEK Cap Nut (Non-Metallic Protective Fastener)

Manufactured using high-performance polymer:

PEEK (Polyether Ether Ketone)

Key engineering benefits:

• Electrically insulating
• Non-magnetic
• Chemical resistant
• Lightweight
• Radiation resistant

Applications:

• Semiconductor equipment
• Chemical processing units
• Medical assemblies
• Electrical insulation zones

SM Fasteners supports precision machining of PEEK cap nuts for specialized OEM programs.

12. Dimensional Logic and Geometry

Cap nut design is governed by geometric relationships ensuring proper load transfer while maintaining dome clearance.

12.1 Critical Dimensions

Symbol	Parameter	Engineering Function
d	Thread diameter	Load capacity
P	Thread pitch	Engagement strength
m	Nut height	Thread engagement
s	Width across flats	Torque transmission
e	Width across corners	Tool clearance
h	Dome height	Thread protection
dc	Bearing diameter	Load distribution

12.2 Standard Metric Dimensional Table (DIN 1587 / ISO Equivalent)

Size	Pitch (mm)	Width Across Flats (mm)	Nut Height m (mm)	Dome Height h (mm)	Bearing Dia (mm)
M6	1.0	10	6	10	11.8
M8	1.25	13	8	13	15.8
M10	1.5	17	10	16	19.6
M12	1.75	19	12	18	21.9
M16	2.0	24	16	24	27.7
M20	2.5	30	20	30	34.6
M24	3.0	36	24	36	41.6

(Dimensions aligned with global procurement tolerances and SM Fasteners production capability.)

12.3 Thread Engagement vs Dome Depth Logic

Engineering requirement:$$Bolt\ Projection < Dome\ Internal\ Height$$

If violated:

• False torque readings occur
• Preload reduces drastically
• Joint loosening risk increases

Recommended safety margin:$$Clearance ≥ 1.5 \times Thread\ Pitch$$

13. Thread Systems and Global Compatibility

Cap nuts must interface with global bolt standards used across EPC supply chains.

13.1 Supported Thread Forms

Thread System	Standard	Region
Metric Coarse	ISO 261 / ISO 965	Global
Metric Fine	ISO 261	Precision assemblies
UNC	ASME B1.1	USA
UNF	ASME B1.1	Aerospace / machinery
BSW	BS 84	Legacy UK systems
BSF	BS 84	Fine British threads

13.2 Thread Tolerance Classes

System	External	Internal
Metric	6g	6H
UNC/UNF	2A	2B
Precision Fit	4H	4g

SM Fasteners maintains calibrated thread gauges traceable to ISO standards.

14. Applicable International Standards

Cap nuts are governed by dimensional and mechanical standards depending on region and application.

14.1 Primary Dimensional Standards

Standard	Description
DIN 1587	Hexagon dome cap nuts
ISO 1587	International equivalent
BS 3692	British metric fasteners
ASME B18.2.2	Inch hex nuts (reference compatibility)

14.2 Mechanical Property Standards

Standard	Scope
ISO 898-2	Carbon steel nut mechanical properties
ASTM A563	Carbon steel structural nuts
ASTM A194	Alloy & stainless steel pressure service
ASTM F594	Stainless steel nuts
ASTM F836	Washer interface compatibility

14.3 Property Classes (ISO System)

Property Class	Proof Load (MPa)	Typical Application
5	Medium duty
8	Structural
10	High strength
12	Heavy engineering

15. Proof Load & Tensile Strength Table

Size	Property Class	Proof Load (kN)	Min Tensile Strength (MPa)
M8	Class 8	18	800
M10	Class 8	29	800
M12	Class 10	46	1000
M16	Class 10	93	1000
M20	Class 10	145	1000
M24	Class 10	210	1000

Values aligned with ISO 898-2 calculations.

16. Dimensional Tolerances

Manufacturing tolerances ensure interchangeability across global suppliers.

Feature	Typical Tolerance
Width across flats	ISO 4759
Height	±0.3 mm
Thread pitch	ISO 965
Concentricity	≤0.1 mm

17. Geometry Influence on Mechanical Performance

Bearing Face Diameter

Controls:

• Surface pressure
• Joint relaxation
• Embedment loss

Dome Thickness

Controls:

• Impact resistance
• Environmental durability

Thread Length

Controls:

• Load distribution
• Fatigue life

18. Interchangeability Considerations for EPC Procurement

EPC buyers require global compatibility.

SM Fasteners designs cap nuts to ensure:

• ISO ↔ DIN interchangeability
• ASTM bolt compatibility
• Cross-regional thread acceptance
• Documentation alignment with project specifications

19. Engineering Selection Guide (Geometry Based)

Condition	Recommended Type
Outdoor corrosion exposure	High crown stainless cap nut
Heavy preload	Heavy hex cap nut
Hygiene requirement	Polished SS cap nut
Electrical insulation	PEEK cap nut
Limited space	Low crown cap nut

20. SM FASTENERS Manufacturing Integration

Under ISO 9001 quality management:

• CNC controlled dome forming
• Forged grain flow optimization
• Precision thread rolling
• Gauge-controlled dimensional inspection
• Custom dome depth manufacturing

Capabilities include:

• Standard production
• EPC custom drawings
• Non-standard thread forms
• Advanced alloy supply

21. Material Engineering for Protective Cap Nuts

Material selection is the most critical engineering decision affecting:

• Mechanical performance
• Corrosion resistance
• Temperature capability
• Fatigue life
• Compliance with project specifications

Protective cap nuts operate in environments ranging from indoor machinery to offshore sour service conditions. The closed dome geometry makes material integrity even more important because trapped moisture or chemicals may accelerate localized corrosion if incorrect materials are selected.

SM Fasteners manufactures cap nuts using certified raw materials with Mill Test Certificates (MTC) traceable to international standards.

21.1 Industrial Material Categories

Material Family	Standards	Typical Grades
Carbon Steel	ISO 898-2 / ASTM A563	Class 5, 8, 10
Alloy Steel	ASTM A194	2H, 7, L7
Stainless Steel	ASTM F594	A2-70, A4-80
Duplex Stainless	ASTM A479	UNS S31803
Super Duplex	ASTM A182	UNS S32750
Nickel Alloys	ASTM B564	Inconel, Monel
High Corrosion Alloy	ASTM B462	Hastelloy
Super Austenitic	ASTM A182	SMO 254
Engineering Polymer	ASTM D6262	PEEK

22. Mechanical Properties — Grade Wise

Material / Grade	Yield Strength (MPa)	UTS (MPa)	Hardness	Temp Limit °C
CS Class 8	640	800	22–32 HRC	300
CS Class 10	900	1000	32–36 HRC	350
Alloy Steel 2H	850	1040	24–35 HRC	425
SS A2-70	450	700	HRB 95	425
SS A4-80	600	800	HRB 100	450
Duplex S31803	550	800	28 HRC max	300
Super Duplex S32750	650	950	32 HRC max	300
Inconel 625	460	830	220 HB	980
Monel 400	240	550	150 HB	480
SMO 254	300	650	96 HRB	400
PEEK	—	—	—	260

23. Material Selection Criteria

Load-Based Selection

Load Condition	Recommended Material
General structural	Carbon steel Class 8
High preload	Alloy steel Class 10
Corrosion exposure	Stainless A4
Offshore seawater	Duplex / Super Duplex
Chemical plant	Hastelloy / SMO 254
High temperature	Inconel
Electrical isolation	PEEK

Environmental Selection Matrix

Environment	Recommended Material
Atmospheric exposure	Zinc plated carbon steel
Marine	A4 Stainless / Duplex
H₂S Sour Service	Duplex (NACE compliant)
Chloride chemical plant	SMO 254
Acid service	Hastelloy
Cryogenic LNG	Austenitic stainless
Electrical equipment	PEEK cap nuts

SM Fasteners supports NACE MR0175 / ISO 15156 compliant material supply.

24. Corrosion Resistance vs Environment

Environment	Carbon Steel	SS 304	SS 316	Duplex	SMO 254	Nickel Alloy
Outdoor humidity	Medium	Good	Excellent	Excellent	Excellent	Excellent
Seawater	Poor	Moderate	Good	Excellent	Superior	Superior
Chlorides	Poor	Moderate	Good	Excellent	Superior	Excellent
Acids	Poor	Moderate	Good	Very Good	Excellent	Outstanding
H₂S	Poor	Moderate	Good	Excellent	Excellent	Excellent
High temperature	Moderate	Good	Good	Good	Good	Outstanding

25. Heat Treatment Processes

Heat treatment ensures mechanical reliability and compliance with ISO property classes.

25.1 Carbon & Alloy Steel Cap Nuts

Process Flow

1. Austenitizing
2. Quenching (oil/polymer)
3. Tempering
4. Stress relief

Engineering Effects

• Increased tensile strength
• Improved fatigue resistance
• Controlled hardness

25.2 Hardness Control (Critical for Cap Nuts)

Because cap nuts are closed-end components:

Excess hardness → crack risk at dome apex.

Service Condition	Maximum Hardness
Standard service	36 HRC
Galvanized fasteners	34 HRC
Sour service	22 HRC max

25.3 Stainless Steel Heat Treatment

• Solution annealing
• Rapid cooling
• Carbide dissolution
• Corrosion resistance restoration

25.4 Duplex & Super Duplex Treatment

Controlled thermal cycle maintains:

• 50/50 ferrite–austenite structure
• Pitting resistance
• SCC resistance

25.5 Nickel Alloy Processing

Nickel alloys are supplied:

• Solution annealed
• Age hardened (where applicable)

Used for extreme temperature and aggressive chemical environments.

26. End-to-End Manufacturing Workflow

SM Fasteners operates integrated manufacturing aligned with ISO 9001 quality management systems.

26.1 Raw Material Verification

Incoming inspection includes:

• Heat number traceability
• Chemical composition verification
• Mechanical certification review
• PMI testing (when required)

Documentation: EN 10204 3.1 MTC

26.2 Forging Process

Preferred manufacturing method.

Advantages:

• Continuous grain flow
• Higher fatigue strength
• Improved dome impact resistance

Process:

1. Bar cutting
2. Cold/Hot forging
3. Dome forming
4. Flash trimming

26.3 Machining Operations

Used for:

• Nickel alloys
• Low volume custom orders
• PEEK fasteners

Includes CNC turning and precision boring.

26.4 Thread Manufacturing

Thread Rolling (Preferred)

Benefits:

• Work hardening
• Improved fatigue resistance
• Smooth surface finish

Thread Cutting

Used for:

• Large diameters
• Exotic alloys
• Custom threads

26.5 Dome Integrity Control

Critical inspection checks:

• Dome thickness uniformity
• Internal cavity depth
• Concentricity with thread axis

Prevents dome cracking under torque.

26.6 Cleaning & Preparation

Processes include:

• Degreasing
• Shot blasting
• Ultrasonic cleaning
• Passivation (stainless)

27. Surface Finishing & Coating Engineering

Surface engineering determines corrosion performance and friction behavior.

27.3 Lubrication & Nut Factor Influence

Typical nut factors:

Condition	Nut Factor (K)
Dry	0.20–0.25
Zinc plated	0.18
Lubricated	0.15
PTFE coated	0.10–0.13

Directly impacts preload accuracy.

28. Hydrogen Embrittlement Control

Preventive measures used by SM Fasteners:

• Controlled plating processes
• Post-bake de-embrittlement
• Hardness monitoring
• Coating selection engineering

Critical for property class ≥10 components.

29. Failure Prevention Through Material Engineering

Failure Mode	Prevention Method
Fatigue	Forged grain flow
SCC	Duplex/Nickel alloys
Galling	Surface coatings
Corrosion	Material upgrade
Embrittlement	Hardness control

30. SM FASTENERS MATERIAL CAPABILITY POSITIONING

SM Fasteners supports global procurement requirements through:

• Certified ISO 9001 manufacturing system
• UKAF accredited quality framework
• MSME registered industrial manufacturing
• Advanced alloy machining capability
• PEEK engineering fastener production
• Full traceability from raw material to dispatch

Custom solutions include:

• Extended dome depth
• Special thread tolerances
• EPC drawing compliance
• High-performance coatings

31. Inspection & Quality Control Philosophy

Protective cap nuts used in EPC, oil & gas, infrastructure, and heavy engineering projects are classified as safety-relevant fastening components.
Because the dome conceals thread ends, inspection control becomes more critical than standard hex nuts.

SM Fasteners integrates inspection through an ISO 9001 certified Quality Management System audited under UKAF accreditation, ensuring manufacturing traceability and compliance verification suitable for global project audits.

31.1 Inspection Stages

Stage	Inspection Activity
Incoming	Raw material verification
In-Process	Forging & dimensional checks
Threading	Gauge validation
Heat Treatment	Hardness & structure verification
Surface Finish	Coating thickness testing
Final Inspection	Mechanical & visual inspection
Dispatch	Documentation verification

32. Dimensional Inspection Requirements

Critical measurements for cap nuts:

• Thread pitch accuracy
• Dome internal clearance
• Concentricity
• Bearing face flatness
• Across-flats dimension

Gauging Tools Used

• GO / NO-GO thread gauges
• Digital height gauges
• Optical comparators
• Coordinate Measuring Machines (CMM)
• Profile projectors

33. Mechanical Testing

Performed in accordance with ISO and ASTM requirements.

Test	Standard	Purpose
Proof Load Test	ISO 898-2	Load capacity validation
Hardness Test	ISO 6508	Heat treatment verification
Tensile Test	ASTM F606	Strength confirmation
Wedge Load Test	ASTM F606	Thread integrity
Torque Test	Internal procedure	Preload validation

34. Non-Destructive Testing (NDT)

Used particularly for alloy steel and critical applications.

Method	Application
Magnetic Particle (MPI)	Crack detection
Dye Penetrant (DPT)	Surface flaws
Ultrasonic Testing	Internal defects
PMI (Positive Material Identification)	Alloy verification

35. Chemical & Metallurgical Verification

SM Fasteners performs:

• Spectrometer chemical analysis
• Grain flow verification (forged nuts)
• Microstructure analysis
• Ferrite testing for duplex steels

36. Certification & Documentation

Global EPC supply requires comprehensive documentation packages.

Standard Documentation

Document	Description
EN 10204 3.1 MTC	Material certification
Heat Treatment Report	Mechanical compliance
Dimensional Inspection Report	Geometry verification
Coating Certificate	Surface treatment validation
Certificate of Conformance	Order compliance
Packing List	Traceability control

Optional:

• EN 10204 3.2 certification
• Third-party inspection (TPI)
• Client witness inspection

37. Traceability System

Each SM Fasteners batch includes:

• Heat number marking
• Production lot identification
• Inspection record linkage
• Packing traceability

Ensures full lifecycle accountability.

38. Industrial Applications of Protective Cap Nuts

38.1 Construction & Structural Steel

Functions:

• Protection of exposed anchor bolts
• Personnel safety at walkways
• Corrosion prevention

Used in:

• Bridges
• Stadiums
• Industrial buildings
• Handrail assemblies

38.2 Oil & Gas Industry

Upstream

• Wellhead equipment
• Drilling structures
• Access platforms

Midstream

• Pipeline supports
• Valve assemblies

Downstream

• Refinery equipment
• Process structures

Duplex, Super Duplex, and Nickel Alloy cap nuts commonly specified.

38.3 Power Generation

Applications include:

• Turbine enclosures
• Generator frames
• Switchyard equipment
• Solar mounting systems

38.4 Petrochemical & Chemical Processing

Closed dome prevents chemical deposition on threads.

Typical environments:

• Acid vapors
• Chloride exposure
• Chemical washdown areas

Materials: SMO 254, Hastelloy, A4 Stainless.

38.5 LNG & Offshore Platforms

Critical advantages:

• Salt spray protection
• Reduced maintenance cycles
• Improved inspection reliability

Coatings commonly used:

• PTFE
• Xylan
• Hot dip galvanizing

38.6 Automotive & Heavy Equipment

Used where safety and aesthetics combine:

• Wheel covers
• Exterior assemblies
• Machinery guards

38.7 Railways & Infrastructure

Applications:

• Passenger safety zones
• Platform railings
• Signal structures

38.8 Shipbuilding & Marine Engineering

Cap nuts prevent marine corrosion initiation at exposed threads.

Materials:

• A4 Stainless
• Duplex
• Nickel alloys

38.9 PEEK Cap Nut Applications

SM Fasteners supplies PEEK protective cap nuts for:

• Electrical insulation
• Semiconductor tooling
• MRI equipment
• Chemical reactors
• Lightweight aerospace assemblies

39. Engineering Tables

39.1 Thread Standards & Tolerances

Thread Type	Standard	Tolerance
Metric	ISO 261 / 965	6H
UNC	ASME B1.1	2B
UNF	ASME B1.1	2B
BSW	BS 84	Medium
BSF	BS 84	Fine

39.2 Tightening Torque Chart (Typical Values)

(Lubricated condition, Property Class 8)

Size	Torque (Nm)	Approx Preload (kN)
M6	10	5
M8	25	12
M10	49	19
M12	85	28
M16	210	55
M20	410	85
M24	710	120

39.3 Preload Calculation — Worked Example

Given

• Bolt: M12
• Torque: 85 Nm
• Nut factor $K = 0.18$K=0.18
• Diameter $D = 0.012\,m$D=0.012m

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

$$F_p = \frac{85}{0.18 \times 0.012}$$

$$F_p ≈ 39,350\,N$$

Result:
Approximate preload = 39 kN

39.4 Dimensional Specification Reference

Size	Pitch	Across Flats	Height	Dome Height
M6	1.0	10	6	10
M8	1.25	13	8	13
M10	1.5	17	10	16
M12	1.75	19	12	18
M16	2.0	24	16	24
M20	2.5	30	20	30
M24	3.0	36	24	36

39.5 Weight Chart (Approximate — SM Fasteners Alignment)

Size	Weight / Piece (kg)	Weight / 100 pcs (kg)
M6	0.004	0.4
M8	0.009	0.9
M10	0.017	1.7
M12	0.030	3.0
M16	0.070	7.0
M20	0.140	14.0
M24	0.250	25.0

39.6 Surface Finish Performance Comparison

Finish	Corrosion Resistance	Friction Stability	Typical Industry
Zinc Plated	Medium	Good	General construction
HDG	High	Moderate	Structural steel
PTFE	Very High	Excellent	Offshore
Dacromet	High	Excellent	Automotive
Passivated SS	Excellent	Good	Chemical
Electropolished	Maximum	Excellent	Hygienic systems

39.7 Material Comparison Table

Material	UTS	Corrosion Resistance	Relative Cost	Typical Use
Carbon Steel	High	Low	Low	Structural
SS 304	Medium	Good	Medium	General industry
SS 316	Medium	Excellent	Medium-High	Marine
Duplex	High	Excellent	High	Offshore
SMO 254	High	Superior	Very High	Chemical plants
Inconel	High	Extreme	Premium	High temperature
PEEK	Moderate	Chemical proof	Premium	Electrical

40. Industrial Packaging & Export Readiness

SM Fasteners supplies export-ready fastening systems.

40.1 Packaging Standards

• VCI anti-corrosion packing
• Thread protection caps
• Heat number labeling
• Moisture barrier bags

40.2 Export Crating

• ISPM-15 compliant wooden crates
• Palletized shipment
• Container optimization
• Shock protection

40.3 Global Supply Documentation

Provided with shipments:

• MTC (EN 10204 3.1 / 3.2)
• Inspection reports
• Heat treatment records
• Coating certificates
• Certificate of Conformance
• Packing & traceability list

41. SM FASTENERS — ENGINEERING & GLOBAL SUPPLY POSITION

Through integrated manufacturing capability, SM Fasteners delivers:

• ISO 9001 certified production
• UKAF accredited quality systems
• MSME registered industrial manufacturing
• Advanced alloy fastener capability
• PEEK engineering solutions
• Custom fastener engineering
• EPC project documentation readiness

Cap Nuts (Protective) manufactured by SM Fasteners are engineered not merely as fastening accessories but as critical reliability components supporting long-life industrial assemblies worldwide.