Self Drilling Screws

1. Industrial Context of Self Drilling Screws

Self drilling screws (SDS), commonly referred to as TEK screws, are engineered fastening systems combining drilling, tapping, and fastening operations into a single installation step.

Unlike conventional bolted assemblies requiring:

• Pre-drilling
• Tapping
• Fastener installation

Self drilling screws eliminate secondary machining operations, significantly improving:

• Installation efficiency
• Alignment accuracy
• Structural reliability
• Labor productivity
• Repeatability under field conditions

Industrial Adoption Drivers

Industry	Engineering Requirement	SDS Advantage
Structural Steel	Fast secondary framing	No pre-drilling
Oil & Gas Modules	Site assembly speed	Reduced installation stages
Power Plants	Sheet & equipment mounting	Controlled preload
Petrochemical	Corrosion resistance	Stainless & alloy grades
Offshore	Limited access installation	One-step fastening
Rail Infrastructure	Vibration-resistant joints	High clamp retention

Within EPC environments, self drilling screws support modular construction philosophy, enabling rapid fabrication while maintaining structural integrity.

SM Fasteners manufactures SDS systems aligned with global project specifications requiring traceability, material certification, and dimensional compliance.

2. Technical Definition

A self drilling screw is a threaded fastener incorporating:

1. Integrated drill point
2. Thread forming or cutting section
3. Load-bearing head
4. Clamping shank

Functional Elements

Component	Engineering Function
Drill Point	Penetrates substrate
Cutting Flutes	Remove chips
Lead Threads	Initiate tapping
Full Threads	Develop clamp force
Head	Transfers torque & load

The drill point geometry is equivalent to a miniature twist drill designed for controlled penetration through metallic substrates.

3. Load Mechanics & Force Behaviour

Self drilling screws operate primarily as preloaded clamping fasteners.

Fundamental Load Principle

The joint integrity depends on clamping force, not screw shear capacity.$$F_p = \frac{T}{K \times d}$$

Where:

• $F_p$​ = Preload (N)
• $T$ = Applied torque (Nm)
• $K$ = Nut factor (friction coefficient)
• $d$ = Nominal diameter (m)

Force Components in Installed Joint

Load Type	Description
Tensile Load	Axial separation force
Shear Load	Lateral sliding
Clamp Force	Compression between members
Bearing Load	Surface contact pressure
Bending Load	Misalignment effects

Torque–Tension Relationship

Only 10–15% of installation torque produces preload.

Energy Distribution	Percentage
Thread Friction	40–45%
Head Friction	40–50%
Useful Clamp Load	10–15%

This explains why lubrication and coating selection critically influence joint performance.

4. Joint Design Principles

Self drilling screw joints must be engineered considering:

4.1 Thread Engagement Requirement

Minimum engagement:$$L_e \geq 1 \times D \quad (Steel)$$

$$L_e \geq 1.5 \times D \quad (Aluminium)$$

4.2 Drill Capacity Matching

Incorrect drill point selection leads to:

• Work hardening
• Tip breakage
• Thread stripping
• Reduced preload

4.3 Joint Stack Design

Key parameters:

• Total material thickness
• Base material hardness
• Coating compatibility
• Thermal expansion mismatch

4.4 Clamp Force Behaviour

Preload must exceed operational loads:$$F_{preload} > F_{external}$$

Failure occurs when external forces unload the joint.

5. Failure Mechanisms

5.1 Fatigue Failure

Caused by fluctuating loads when preload insufficient.

Mitigation:

• Correct torque
• Hardened washers
• Controlled lubrication

5.2 Shear Failure

Occurs when joint slips.

Design Rule:
Shear loads must transfer via friction, not screw shank.

5.3 Hydrogen Embrittlement

Risk for hardened carbon steel SDS.

Controls at SM Fasteners:

• Baking after electroplating
• Hardness control
• ISO 4042 compliant finishing

5.4 Stress Corrosion Cracking

Common in:

• Chloride environments
• Offshore installations
• Chemical plants

Solution:

• Duplex stainless
• Nickel alloys
• PEEK fasteners where metallic corrosion risk exists

6. Functional Role in Industrial Assemblies

Self drilling screws are primarily used for:

• Thin steel-to-steel connections
• Sheet metal assemblies
• Equipment housings
• Roofing and cladding systems
• Cable tray installations
• HVAC structures
• Offshore module fabrication

They enable repeatable torque-controlled installation, making them suitable for automated or semi-automated assembly lines.

7. Preload Calculation — Worked Example

Given:

• Screw: M6 Self Drilling Screw
• Torque: 10 Nm
• Nut Factor: 0.20

$$F_p = \frac{10}{0.20 \times 0.006}$$

$$F_p = 8333 N$$

Result: Approximate preload = 8.3 kN

This preload ensures resistance against vibration-induced loosening.

8. Engineering Advantages Over Conventional Fastening

Parameter	Conventional Screw	Self Drilling Screw
Pre-drilling	Required	Not required
Installation Time	High	Low
Alignment Error	Possible	Minimal
Labor Dependency	High	Reduced
Field Productivity	Moderate	High

9. Role Within SM Fasteners Manufacturing Philosophy

SM Fasteners integrates:

• Certified material sourcing
• Controlled thread forming
• ISO 9001 process validation
• Global dimensional compliance
• Engineering traceability

The objective is delivering procurement-ready fasteners suitable for EPC documentation review and third-party inspection.

10. Product Architecture of Self Drilling Screws

Self drilling screws are engineered systems where geometry directly determines drilling efficiency, torque transmission, load capacity, and service life.

Unlike conventional screws, every geometric parameter performs a defined mechanical function:

• Drill point → penetration capability
• Thread profile → load development
• Head geometry → torque transfer & sealing
• Drive interface → installation repeatability

SM Fasteners manufactures SDS configurations optimized for industrial assembly tolerances and global interchangeability requirements.

11. Classification of Self Drilling Screws

11.1 Based on Head Configuration

Head Type	Engineering Purpose	Typical Application
Hex Washer Head	High torque transmission	Structural steel, roofing
Pan Head	Controlled clamp area	Electrical panels
Countersunk (CSK)	Flush surface	Architectural assemblies
Modified Truss Head	Large bearing surface	Thin sheet metal
Wafer Head	Low-profile fastening	HVAC systems
Flat Head	Embedded installations	Equipment housings

Hex washer head designs dominate industrial applications due to superior torque capacity and washer sealing performance.

11.2 Based on Drive System

Drive Type	Torque Capacity	Industrial Suitability
Hex External	Excellent	Structural & EPC
Phillips	Moderate	Light assemblies
Torx (Star)	Very High	Automated production
Square Drive	High	OEM fabrication
Combination Drive	Flexible	Maintenance work

Engineering Trend:
EPC contractors increasingly specify Torx drives to reduce cam-out and torque variability.

11.3 Based on Drill Point (TEK Number)

The drill point determines maximum drilling thickness capability.

TEK Point	Drill Capacity (Steel Thickness)	Application
TEK 1	Up to 2 mm	Sheet metal
TEK 2	2–3 mm	Light steel
TEK 3	3–5 mm	Structural sheet
TEK 4	6–8 mm	Heavy steel
TEK 5	8–12 mm	Structural members

Selection error between drill capacity and material thickness is the primary cause of installation failure.

11.4 Based on Thread Type

Thread Form	Functional Behavior
Self-Tapping Thread	Forms mating thread
Fine Thread	Higher clamp load
Coarse Thread	Faster installation
Twin Lead Thread	Reduced installation time
Hi-Lo Thread	Soft material compatibility

12. Dimensional Logic & Engineering Geometry

Self drilling screw performance depends on proportional relationships between:

• Diameter
• Thread pitch
• Drill flute length
• Head bearing surface

12.1 Standard Dimensional Specification Table

(Typical SM Fasteners Industrial Range)

Size	Nominal Dia (mm)	Pitch (mm)	Head Dia (mm)	Drill Length (mm)	Length Range (mm)
#8	4.2	1.41	8.5	5	13–50
#10	4.8	1.59	10.5	6	16–75
#12	5.5	1.81	11.0	7	20–100
#14	6.3	2.11	13.5	8	25–150
M5	5.0	0.8	10	6	16–80
M6	6.0	1.0	12	8	20–120

Dimensional tolerances maintained according to ISO and DIN thread standards.

12.2 Thread Engagement Principles

Minimum thread engagement:

Base Material	Engagement Requirement
Structural Steel	≥1× diameter
Aluminium	≥1.5× diameter
Stainless Sheet	≥1.2× diameter

12.3 Drill Point Geometry Logic

Key design parameters:

• Point angle: 135°–145°
• Flute clearance angle
• Chip evacuation path
• Cutting edge hardness

Improper geometry results in excessive torque and thermal damage.

13. International Standards Compliance

Self drilling screws used in global EPC projects must conform to internationally accepted dimensional and mechanical standards.

SM Fasteners manufactures in accordance with multi-standard interchangeability requirements.

13.1 ISO Standards

Standard	Description
ISO 1478	Thread forming screw threads
ISO 15480	Self drilling screw performance
ISO 898-1	Mechanical properties
ISO 4042	Electroplated coatings
ISO 3506	Stainless steel fasteners
ISO 965	Thread tolerances

13.2 DIN Standards

DIN Standard	Scope
DIN 7504	Self drilling screws
DIN 7981	Pan head screws
DIN 7982	Countersunk screws
DIN 7500	Thread forming screws

DIN 7504 remains the most widely referenced SDS standard globally.

13.3 ASTM Standards

ASTM	Description
ASTM C1513	Self drilling tapping screws
ASTM F568M	Mechanical properties metric
ASTM A240	Stainless steel material
ASTM B633	Zinc coating
ASTM A193	Alloy fasteners (high temp)

13.4 British Standards (BS)

BS Standard	Application
BS 4174	Self tapping screws
BS EN ISO 1478	Thread profile
BS EN 10204	Inspection documentation

14. Thread Standards & Tolerances

Thread System Compatibility Table

Thread System	Standard	Typical Use
Metric	ISO 261 / ISO 965	Global projects
UNC	ASME B1.1	North America
UNF	ASME B1.1	Aerospace & vibration
BSW	BS 84	Legacy UK equipment
BSF	BS 84	Fine pitch applications

Tolerance classes typically supplied:

• 6g external thread (metric)
• 2A UNC
• 2A UNF

15. Mechanical Property Classes

Self drilling screws require hardened drill tips and controlled core ductility.

Property Class	Ultimate Tensile Strength (MPa)	Yield Strength (MPa)	Application
Class 8.8	800	640	General structural
Class 10.9	1040	940	High strength
Class 12.9	1220	1100	Heavy duty
A2-70	700	450	Corrosion resistant
A4-80	800	600	Offshore

SM Fasteners maintains hardness gradients ensuring drill tip hardness exceeds thread body hardness.

16. Proof Load & Tensile Strength Table

Size	Proof Load (kN)	Tensile Load (kN)
#8	6.0	8.0
#10	8.5	11
#12	11	15
#14	14	19
M5	9	12
M6	13	18

Values depend on property class and material grade.

17. Dimensional Interchangeability Considerations

EPC procurement frequently demands cross-standard equivalence.

Engineering checks required:

• Head height compatibility
• Washer diameter equivalence
• Drive engagement depth
• Thread flank angle consistency
• Drill capacity equivalence

SM Fasteners supports multi-standard drawings and project-specific dimensional approvals.

18. Engineering Selection Criteria

Self drilling screw selection must consider:

Mechanical Factors

• Required clamp force
• Base metal thickness
• Joint fatigue exposure

Environmental Factors

• Corrosive media
• Temperature exposure
• Galvanic compatibility

Installation Factors

• Access limitations
• Tool torque capability
• Automation requirements

19. Procurement Specification Example

Typical EPC specification may include:

• DIN 7504 K
• Property Class 10.9
• Zinc Flake Coating
• ISO 965 Thread Tolerance
• EN 10204 3.1 Certification
• PMI Verification
• Traceability Marking

SM Fasteners engineering team supports full technical submittal packages aligned with project documentation procedures.

20. Materials Engineering for Self Drilling Screws

Material selection is the primary engineering determinant governing:

• Mechanical strength
• Drill performance
• Corrosion resistance
• Temperature capability
• Service life reliability

Self drilling screws require a dual-performance material behavior:

1. High hardness at drill point
2. Adequate ductility in threaded shank

SM Fasteners supplies a full industrial material range supporting global EPC specifications and severe-service applications.

21. Industrial Material Grades

21.1 Carbon Steel Grades

Material	Standard	Typical Hardness	Application
C1022	SAE / ASTM	32–40 HRC	Standard SDS
C1018	ASTM	Medium	Sheet metal
Boron Steel	DIN	High hardenability	Heavy drilling

Advantages:

• High strength
• Economical production
• Excellent drill performance

Limitations:

• Requires protective coating
• Susceptible to corrosion

21.2 Alloy Steel Grades

Grade	Standard	Service Condition
4140	ASTM A29	Structural fastening
4340	ASTM	High fatigue loads
B7 Equivalent	ASTM A193	Elevated temperature

Used where:

• Higher preload required
• Cyclic loading present
• Structural safety critical

21.3 Stainless Steel Grades

Grade	Standard	Corrosion Resistance	Application
A2-70 (304)	ISO 3506	Atmospheric	Construction
A4-80 (316)	ISO 3506	Marine	Offshore
410 SS	ASTM	Hardenable	Drill point screws
17-4 PH	ASTM A564	High strength	Critical equipment

Stainless SDS often use bi-metal construction:

• Hardened carbon steel drill tip
• Stainless body

21.4 Duplex & Super Duplex Stainless Steel

Grade	PREN Value	Environment
Duplex 2205	~35	Chloride exposure
Super Duplex 2507	>40	Offshore subsea

Advantages:

• High strength
• Exceptional SCC resistance
• Long service life

21.5 Nickel & High-Performance Alloys

Material	Max Temp	Industrial Use
Inconel 625	980°C	LNG & turbine
Inconel 718	700°C	Aerospace
Hastelloy C276	Acid resistant	Chemical plants
Monel 400	Seawater	Marine
Incoloy 825	Sour service	Oil & Gas
SMO 254	Chloride systems	Desalination

SM Fasteners manufactures specialty alloy fasteners compliant with NACE MR0175 / ISO 15156 sour service requirements.

21.6 PEEK Fasteners (Advanced Engineering Polymer)

Property	Value
Continuous Temp	260°C
Corrosion Resistance	Excellent
Electrical Insulation	Outstanding
Chemical Resistance	Exceptional

Applications:

• Semiconductor manufacturing
• Chemical reactors
• Electrical insulation zones
• Anti-galvanic assemblies

PEEK SDS solutions are engineered where metallic fasteners create contamination or galvanic corrosion risk.

22. Material Comparison Table

Material	UTS (MPa)	Yield (MPa)	Corrosion Resistance	Relative Cost	Typical Industry
Carbon Steel	800–1200	High	Low	Low	Construction
Alloy Steel	1000–1400	Very High	Moderate	Medium	Structural
SS 304	700	Medium	Good	Medium	Infrastructure
SS 316	800	High	Excellent	Higher	Offshore
Duplex 2205	900	Very High	Excellent	High	Oil & Gas
Inconel 625	850	High	Exceptional	Premium	LNG
PEEK	100	Low	Absolute	Premium	Electronics

23. Heat Treatment Processes

Key Objective:

Heat treatment creates the essential performance characteristic of self drilling screws.

Hard drill point + Tough load-bearing core

23.1 Process Sequence

1. Austenitizing
2. Oil or polymer quenching
3. Tempering
4. Surface stress relief

23.2 Typical Hardness Control

Zone	Hardness Requirement
Drill Tip	52–58 HRC
Thread Body	32–40 HRC
Head	28–36 HRC

Hardness gradient prevents brittle fracture.

23.3 Hydrogen Embrittlement Prevention

SM Fasteners controls risk through:

• Post plating bake (200°C / 4 hrs)
• Hardness monitoring
• ISO 4042 process validation

Essential for high-strength SDS used in structural environments.

24. End-to-End Manufacturing Workflow

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

24.1 Raw Material Verification

Incoming material inspection includes:

• Mill Test Certificate verification
• Chemical composition analysis
• PMI testing (Positive Material Identification)
• Mechanical property validation

Traceability maintained via heat number tracking.

24.2 Cold Heading / Forging

Cold heading advantages:

• Grain flow alignment
• Higher fatigue strength
• Material utilization efficiency

Forging forms:

• Head geometry
• Washer integration
• Drive recess

24.3 Drill Point Formation

Specialized tooling creates:

• Cutting lips
• Flute geometry
• Chip evacuation channels

Critical for drilling efficiency.

24.4 Thread Rolling vs Thread Cutting

Method	Engineering Benefit
Thread Rolling	Increased fatigue life
Thread Cutting	Used for hard alloys

Rolled threads produce compressive residual stresses improving durability.

24.5 Heat Treatment Integration

Continuous furnaces ensure:

• Uniform hardness
• Controlled microstructure
• Reduced distortion

24.6 Surface Preparation

Before coating:

• Alkaline cleaning
• Pickling
• Shot blasting
• Surface activation

24.7 Final Inspection & Sorting

Automated optical sorting verifies:

• Length
• Head height
• Thread pitch
• Drive integrity
• Tip geometry

25. Surface Engineering & Coatings

Surface finishing determines corrosion resistance and torque behavior.

25.1 Coating Types

Coating	Thickness	Salt Spray Resistance	Application
Zinc Plating	5–12 µm	72–120 hrs	Indoor
HDG	40–80 µm	600+ hrs	Structural
Zinc Flake	8–12 µm	1000+ hrs	Automotive
Dacromet	Thin	High	Offshore
Mechanical Galvanized	Medium	Moderate	Construction
Passivated Stainless	—	Excellent	Marine

25.2 Surface Finish Performance Comparison

Finish	Corrosion Resistance	Friction Stability	Hydrogen Risk
Zinc Electroplate	Moderate	Stable	Medium
Zinc Flake	Excellent	Very Stable	Low
HDG	Excellent	Variable	Low
Phosphate	Low	Excellent	Very Low
PTFE Topcoat	High	Excellent	Very Low

25.3 Corrosion Resistance vs Environment

Environment	Recommended Material / Coating
Indoor Dry	Zinc Plated
Outdoor Urban	Zinc Flake
Marine Atmosphere	SS 316 / Duplex
Offshore Platform	Super Duplex
Chemical Plant	Hastelloy
H₂S Sour Service	Incoloy / NACE compliant
Electrical Isolation	PEEK

26. Mechanical Properties — Grade Wise

Property Class	Hardness	Tensile Strength (MPa)	Typical Use
8.8	22–32 HRC	800	General
10.9	32–39 HRC	1040	Structural
12.9	39–44 HRC	1220	Heavy duty
A2-70	HRB 95	700	Corrosion resistant
A4-80	HRB 100	800	Marine

27. Engineering Considerations for Severe Service

Critical selection parameters:

• Temperature cycling
• Chloride exposure
• Galvanic compatibility
• Installation torque control
• Inspection traceability

SM Fasteners engineering supports custom fastener design incorporating advanced alloys and polymer solutions tailored to project specifications.

28. Integration with SM Fasteners Quality System

Manufacturing controlled under:

• ISO 9001 certified QMS
• UKAF accredited inspection processes
• Batch traceability system
• Documented heat treatment validation
• Project-specific material control plans

Ensuring global procurement readiness for EPC, OEM, and infrastructure projects.

29. Inspection & Quality Control Framework

Self drilling screws used in EPC, oil & gas, infrastructure and heavy engineering projects are classified as critical joining components.
Therefore, inspection must verify:

• Dimensional compliance
• Mechanical performance
• Material integrity
• Surface treatment reliability
• Traceability documentation

SM Fasteners integrates inspection throughout the manufacturing lifecycle under an ISO 9001 certified Quality Management System with UKAF-accredited practices.

29.1 Incoming Material Inspection

Inspection	Purpose
Mill Test Certificate Review	Verify heat chemistry
PMI Testing	Confirm alloy grade
Spectro Analysis	Elemental validation
Hardness Testing	Process suitability
Visual Examination	Surface defects

Each production batch remains traceable to raw material heat number.

29.2 In-Process Inspection

Control stages include:

• Head formation verification
• Thread pitch measurement
• Drill tip geometry inspection
• Concentricity check
• Rolling integrity validation

Statistical Process Control (SPC) ensures dimensional stability.

29.3 Final Inspection & Testing

Test	Standard Reference
Tensile Testing	ISO 898 / ASTM F606
Proof Load Test	ISO 898
Torque Test	DIN 7504
Drill Performance Test	ISO 15480
Coating Thickness	ISO 2178
Salt Spray Test	ASTM B117
Hardness Test	ISO 6508
Thread Gauge Inspection	ISO 1502

29.4 Non-Destructive Examination (NDT)

Where project specifications require:

• Magnetic Particle Inspection (MPI)
• Dye Penetrant Testing (DPT)
• Ultrasonic Examination (UT)
• Eddy Current inspection (special alloys)

29.5 Documentation & Certification

SM Fasteners provides full project documentation packages:

Document	Standard
EN 10204 3.1 MTC	Mandatory supply
EN 10204 3.2 Certification	Third-party validated
Heat Treatment Reports	Furnace traceability
Coating Compliance	ISO 4042
Inspection Reports	Dimensional & mechanical
Certificate of Conformance	Project requirement

30. Failure Analysis & Reliability Engineering

Typical failure modes evaluated during QA review:

Failure Mode	Root Cause	Preventive Control
Drill Tip Breakage	Incorrect hardness	Heat treatment control
Thread Stripping	Over-torque	Torque specification
Fatigue Failure	Low preload	Joint design review
Hydrogen Embrittlement	Improper plating	Baking procedure
Galvanic Corrosion	Material mismatch	Alloy selection

Engineering feedback loops allow corrective action within ISO 9001 systems.

31. Industry Applications

Self drilling screws serve across multiple high-reliability industrial sectors.

31.1 Construction & Structural Steel

Applications:

• Secondary framing
• Roofing systems
• Steel decking
• Facade systems

Engineering Requirement:
Fast installation with predictable clamp load.

31.2 Oil & Gas Industry

Upstream

• Rig structures
• Equipment enclosures

Midstream

• Pipeline accessories
• Compressor housings

Downstream

• Refinery panels
• Instrument mounting

Materials frequently specified:

• A4 stainless
• Duplex
• Incoloy
• NACE compliant alloys

31.3 Power Generation

• Turbine housing panels
• Cable tray systems
• Solar mounting
• Nuclear auxiliary systems

Thermal cycling resistance becomes primary selection criteria.

31.4 Petrochemical & Chemical Processing

Requirements:

• Acid resistance
• Chloride protection
• Stress corrosion resistance

Preferred materials:
Hastelloy, SMO 254, Duplex stainless.

31.5 LNG & Offshore Structures

Design considerations:

• Salt spray exposure
• Dynamic vibration
• Maintenance accessibility

Super Duplex and high-performance coatings commonly specified.

31.6 Automotive & Heavy Equipment

• Cab structures
• Equipment panels
• Agricultural machinery

Automation-compatible Torx drive systems are preferred.

31.7 Railways & Infrastructure

• Signaling equipment
• Bridge accessories
• Noise barriers
• Electrical enclosures

High fatigue resistance essential.

31.8 Shipbuilding & Marine

Challenges:

• Continuous seawater exposure
• Galvanic corrosion
• Cyclic loading

Typical materials:
A4-80, Duplex, Monel.

31.9 PEEK Fastener Applications

Used where metallic fasteners are unsuitable:

• Semiconductor plants
• Chemical reactors
• Electrical insulation zones
• MRI equipment
• Corrosion-sensitive assemblies

SM Fasteners manufactures engineered PEEK solutions supporting specialty industrial environments.

32. Export Capability & Global Supply Readiness

SM Fasteners supplies self drilling screws globally with export-ready logistics aligned to EPC procurement procedures.

32.1 Industrial Packaging

Packaging Type	Purpose
VCI Packaging	Corrosion protection
Thread Caps	Mechanical protection
Heat-Sealed Bags	Moisture barrier
Batch Labeling	Traceability
Palletized Loads	Safe handling

32.2 Export Crating

• ISPM-15 compliant fumigated wooden crates
• Containerized bulk shipment
• Custom project kitting
• Barcode traceability

32.3 Export Documentation

Typical supply documentation:

• Commercial Invoice
• Packing List
• Certificate of Origin
• EN 10204 3.1 / 3.2
• Inspection Release Note
• Test Certificates
• Heat Treatment Records
• Coating Compliance Reports

33. ENGINEERING TABLES

33.1 Mechanical Properties Table

Property Class	Yield Strength MPa	Tensile Strength MPa	Hardness
8.8	640	800	22–32 HRC
10.9	940	1040	32–39 HRC
12.9	1100	1220	39–44 HRC
A2-70	450	700	HRB 95
A4-80	600	800	HRB 100

33.2 Tightening Torque Chart (Typical Values)

Size	Grade 8.8 Dry (Nm)	Lubricated (Nm)
#8	4	3
#10	6	4.5
#12	9	7
#14	14	10
M5	7	5
M6	12	9

33.3 Preload Calculation Formula

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

Example — M6 Screw

Torque = 12 Nm
Nut Factor = 0.2$$F = \frac{12}{0.2 \times 0.006} = 10,000N$$

Approximate clamp load = 10 kN

33.4 Thread Standards & Tolerances

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

33.5 Surface Finish Performance Comparison

Coating	Salt Spray (hrs)	Friction Stability	Use
Zinc Plated	72–120	Good	Indoor
Zinc Flake	1000+	Excellent	Automotive
HDG	600+	Moderate	Structural
PTFE	High	Excellent	Chemical
Stainless Passive	Excellent	Stable	Marine

33.6 Corrosion Resistance vs Environment

Environment	Recommended Material
Indoor	Zinc plated carbon steel
Outdoor	Zinc flake
Marine	SS 316
Offshore	Super Duplex
Acidic	Hastelloy
H₂S	Incoloy / NACE
Electrical Isolation	PEEK

33.7 Weight Chart — Self Drilling Screws

(Aligned with SM Fasteners Production Data — Approximate)

Size	Length (mm)	Weight / Piece (g)	Weight / 100 pcs (kg)
#8	25	3.2	0.32
#10	25	4.5	0.45
#12	38	7.8	0.78
#14	50	12.5	1.25
M5	30	5.2	0.52
M6	40	9.8	0.98

34. Procurement & Engineering Selection Checklist

Engineers should confirm:

• Required clamp load
• Base material thickness
• Drill capacity (TEK number)
• Corrosion environment
• Mechanical property class
• Coating requirement
• Inspection documentation level
• Traceability requirement

SM Fasteners provides technical support for complete engineering submittal approval.

ENGINEERING CONCLUSION

Self drilling screws represent a highly engineered fastening solution integrating:

• Drilling
• Thread formation
• Structural clamping

When designed, manufactured, and inspected under controlled systems such as those implemented by SM Fasteners, they deliver:

• Predictable mechanical performance
• Global standards compliance
• Reliable installation efficiency
• Long-term structural integrity

Through ISO 9001 certified manufacturing, UKAF-accredited inspection systems, advanced material capability—including Duplex, Nickel Alloys, and PEEK—and full export documentation readiness, SM Fasteners demonstrates capability aligned with global EPC, OEM, and industrial procurement requirements.