4.6
Strength: 400 MPa nominal tensile class
Reference: 240 MPa nominal yield relationship
Nut pairing: Compatible ISO 898-2 nut class
General carbon-steel fasteners
Fastener Identification
Bolt head markings chart.
Visual reference for common metric property classes, stainless markings, SAE grades and ASTM bolting systems. Manufacturer identification normally appears with the grade mark where the governing standard requires it.
5.6
Strength: 500 MPa nominal tensile class
Reference: 300 MPa nominal yield relationship
Nut pairing: Compatible ISO 898-2 nut class
General machinery / fabrication
8.8
Strength: 800 MPa nominal tensile class
Reference: 640 MPa nominal yield relationship
Nut pairing: Class 8/10 nut as specified
High-tensile metric bolting
10.9
Strength: 1000 MPa nominal tensile class
Reference: 900 MPa nominal yield relationship
Nut pairing: Class 10 or approved matching nut
Higher-strength machinery / structural applications
12.9
Strength: 1200 MPa nominal tensile class
Reference: 1080 MPa nominal yield relationship
Nut pairing: Approved high-strength matching nut
Socket / very high-strength applications
A2-70
Strength: 700 MPa property class
Reference: A2 stainless family
Nut pairing: A2 nut to ISO 3506-2 as specified
General stainless fastening
A4-80
Strength: 800 MPa property class
Reference: A4 / molybdenum-bearing stainless family
Nut pairing: A4 nut to ISO 3506-2 as specified
Higher-strength corrosion-resistant fastening
3 lines
Strength: Medium-carbon quenched & tempered
Reference: Common minimum tensile class around 120 ksi by size range
Nut pairing: SAE compatible nut grade
Automotive / machinery inch fasteners
6 lines
Strength: Alloy/medium-carbon quenched & tempered
Reference: Common minimum tensile class around 150 ksi by size range
Nut pairing: SAE compatible nut grade
High-strength inch fasteners
No radial lines
Strength: Low/medium-carbon steel
Reference: Lower-strength SAE general fastener
Nut pairing: SAE compatible nut grade
Light-duty inch fasteners
A307
Strength: Carbon-steel bolt system
Reference: Strength requirements depend on A/B grade and size
Nut pairing: Compatible nut per project / ASTM system
General structural / equipment bolting
A325
Strength: High-strength structural bolt
Reference: Structural mechanical requirements vary by diameter/type
Nut pairing: Approved structural nut + F436 washer system
Preloaded / bearing structural joints
A490
Strength: Higher-strength structural bolt
Reference: Higher tensile class than A325
Nut pairing: Approved structural nut + F436 washer system
High-strength structural joints
B7
Strength: Cr-Mo alloy bolting
Reference: Pressure / temperature-service mechanical properties
Nut pairing: ASTM A194 2H commonly paired
Flanges, valves, pressure equipment
B8 / B8M
Strength: Stainless bolting grades
Reference: Class/condition controls final strength
Nut pairing: ASTM A194 8 / 8M commonly paired
Stainless pressure-service bolting
L7
Strength: Low-temperature alloy bolting
Reference: Impact/test requirements apply by specification
Nut pairing: ASTM A194 grade as specified
Low-temperature pressure service
36
Strength: Anchor-bolt material grade
Reference: 36 ksi minimum yield designation
Nut pairing: Nut/washer per project and specification
General anchor bolts
55
Strength: Anchor-bolt material grade
Reference: 55 ksi minimum yield designation
Nut pairing: Nut/washer per project and specification
Higher-strength anchor bolts
105
Strength: Anchor-bolt material grade
Reference: 105 ksi minimum yield designation
Nut pairing: Nut/washer per project and specification
High-strength anchor bolts
Identification rule: head marking alone is not sufficient for acceptance. Verify manufacturer identification, dimensional standard, grade/material specification, thread series, coating, certificate and project requirements.