Fastener Identification Markings
Fastener head markings are standardized to provide critical information regarding mechanical properties, material composition, and manufacturing standards.
In the United States, these identification requirements are primarily governed by ASTM International and the Society of Automotive Engineers (SAE). Markings may indicate grade (SAE), property class, or specification (ASTM), and are required to distinguish between carbon steel, alloy steel, and stainless steel fasteners of varying strength levels. Proper identification ensures compliance with engineering specifications, traceability, and safety in service.
The tables below summarizes common head markings in accordance with ASTM and SAE standards, serving as a reference for selecting and verifying fasteners in industrial applications.
*Please note the bolt heads may also include the manufacturer's identification stamp, especially with high strength bolts.
Things To Consider
Prior to selecting or installing any fastener, it is critical to evaluate its mechanical properties—tensile strength, proof load, and yield strength—to ensure the fastener maintains structural integrity and performs reliably under operational loads.
Tensile strength is the maximum stress that a fastener material can withstand before permanent deformation or fracture occurs. It is determined through standardized mechanical testing, where controlled axial loads are applied until failure. Tensile strength provides a quantitative measure of the fastener’s ultimate load-bearing capacity and is essential for verifying suitability for the intended application.
Proof load represents the maximum load a fastener can sustain without undergoing permanent deformation. This value is typically expressed as a percentage of the material’s tensile strength and is verified through mechanical testing. Selecting a fastener with an appropriate proof load ensures it can safely carry expected operational stresses without compromising structural performance.
Yield strength defines the stress at which a fastener begins to deform plastically, marking the transition from elastic to permanent deformation. Knowledge of the yield strength allows engineers to determine safe working loads and design margins, ensuring that fasteners retain elasticity under normal service conditions.
ASTM Markings
| Grade Marking | Specifications | Material and Treatment | Nominal Size (in.) | Mechanical Properties | Hardness Rockwell | |||||
| Proof Load Min (ksi) | Yield Strength Min (ksi) | Tensile Strength Min (ksi) | Elong % Min | RA % Min | Min | Max | ||||
 | A307 Grade A | Low or Medium Carbon Steel | 1/4" - 4" | - | - | 60 | 18 | - | B69 | B100 |
 | A307 Grade B | Low or Medium Carbon Steel | 1/4" - 4" | - | - | 60 min 100 max | 18 | - | B69 | B95 |
 | A193/A320 Grade B8 Class 1 | AISI SS304 Stainless | No Restrictions | - | 30 | 75 | 30 | 50 | - | B96 |
 | A193/A320 Grade B8 Class 2 | AISI SS304 Stainless | Up To 3/4 | - | 100 | 125 | 12 | 35 | - | C35 |
| 7/8-1 | 80 | 115 | 15 | 35 | ||||||
| 1-1/8 - 1-1/4 | 65 | 105 | 20 | 35 | ||||||
| 1-3/8 - 1-1/2 | 50 | 100 | 28 | 45 | ||||||
 | A193/A320 Grade B8M | AISI SS316 Stainless | No Restrictions | - | 30 | 75 | 30 | 50 | - | B96 |
 | A193/A320 Grade B8M Class 2 | AISI SS316 Stainless | Up To 3/4 | - | 95 | 110 | 15 | 45 | - | C35 |
| 7/8-1 | 80 | 100 | 20 | 45 | ||||||
| 1-1/8 - 1-1/4 | 65 | 95 | 25 | 45 | ||||||
| 1-3/8 - 1-1/2 | 50 | 90 | 30 | 45 | ||||||
 | A449 Type 1 | Medium Carbon Alloy Steel, Q & T | 1/4" - 1" | 85 | 92 | 120 | 14 | 35 | C25 | C34 |
| 1 1/8" - 1 1/2" | 74 | 81 | 105 | C19 | C30 | |||||
| 1 5/8" - 3" | 55 | 58 | 90 | B91 | B100 | |||||
 | A449 Type 3 | Weathering Steel, Q & T | 1/4" - 1" | 85 | 92 | 120 | 14 | 35 | C25 | C34 |
| 1 1/8" - 1 1/2" | 74 | 81 | 105 | C19 | C30 | |||||
| 1 5/8" - 3" | 55 | 58 | 90 | B91 | B100 | |||||
 | A193 Grade B7 | Medium Carbon Alloy Steel, Q & T | 1/4" - 2 1/2" | - | 105 | 125 | 16 | 50 | - | C35 |
| 2 5/8" - 4" | 95 | 115 | 16 | |||||||
| 4 1/8" - 7" | 75 | 100 | 18 | |||||||
 | A354 Grade BC | Medium Carbon Alloy Steel, Q & T | 1/4" - 2 1/2" | 105 | 109 | 125 | 16 | 50 | C26 | C36 |
| Over 2 1/2" | 95 | 99 | 115 | 16 | 45 | C22 | C33 | |||
 | A350 Grade L7 | AISI 4140, 4142, or 4145 | 1/4"-2 1/2" | - | 105 | 125 | 16 | 50 | - | - |
 | A350 Grade L43 | AISI 4340 | 1/4" - 4" | - | 105 | 125 | 16 | 50 | - | - |
 | A354 Grade BD | Medium Carbon Alloy Steel, Q & T | 1/4" - 4" | - | 130 | 150 min 173 max | 14 | 40 | C33 | C38 |
 | F3125 Grade A325 Type 1 | Medium Carbon Q & T | 1/2" - 1 1/2" | 85 | 92 | 120 | 14 | 35 | C24 | C35 |
 | F3125 Grade A325 Type 3 | Atmospheric Corrosion Resistant Steel, | 1/2" - 1 1/2" | 85 | 92 | 120 | 14 | 35 | C24 | C35 |
 | F3125 Grade A490 Type 1 | Medium Carbon Alloy Steel, Q & T | 1/2" - 1 1/2" | 120 | 130 | 150 min 173 max | 14 | 40 | C33 | C38 |
 | F3125 Grade A490 Type 3 | Atmospheric Corrosion Resistant Steel, Q & T | 1/2" - 1 1/2" | 120 | 130 | 150 min 173 max | 14 | 40 | C33 | C38 |
SAE Markings
| Grade Marking | Specifications | Material and Treatment | Nominal Size (in.) | Mechanical Properties | Hardness Rockwell | |||||
| Proof Load Min (ksi) | Yield Strength Min (ksi) | Tensile Strength Min (ksi) | Elong % Min | RA % Min | Min | Max | ||||
 | SAE J429 Grade 1 | Low or Medium Carbon Steel | 1/4" - 1 1/2" | 33 | 36 | 60 | 18 | 35 | B70 | B100 |
| SAE J429 Grade 2 | Low or Medium Carbon Steel | 1/4" - 3/4" | 55 | 57 | 74 | 18 | 35 | B80 | B100 |
| 7/8" - 3/4" | 33 | 36 | 60 | 18 | B70 | B100 | ||||
 | SAE J429 Grade 5 | Medium Carbon Steel, Q & T | 1/4" - 1" | 85 | 92 | 120 | 14 | 35 | C25 | C34 |
| 1 1/8" - 1 1/2" | 74 | 81 | 105 | C19 | C30 | |||||
 | SAE J429 Grade 8 | Medium Carbon Alloy Steel, Q & T | 1/4" - 1 1/2" | 120 | 130 | 150 | 12 | 35 | C33 | C39 |