Visual bolt grade finder
Which Bolt Grade Do You Have?
Match the marks on the bolt head to these common SAE and metric examples. Select a marking to see its strength values.
† Size matters: illustrated tensile values are for the first applicable size band; choose the actual diameter range below. No lines ≠ confirmed Grade 2. Manufacturer symbols are not grade lines.
Strength lookup by grade & size
Reference minimum stressesThese are material stress minima, not allowable bolt loads or torque values.
View the full chart row ↓Identification is not certification: markings alone cannot establish traceability, allowable load, torque, or suitability for replacement. Confirm the full specification, thread and application.
Inch-series · SAE J429
SAE Bolt Grade Chart (2, 5 & 8)
3 radial lines = Grade 5; 6 radial lines = Grade 8. Strength values below are minimum reference stresses in ksi (1 ksi = 1,000 psi). Choose the correct nominal diameter band. Source and limitations.
No matching grade. Clear search to restore all rows.
Swipe across the table on mobile to view all strength columns →
The table scrolls horizontally on narrow screens. The left column names the grade.
| SAE Grade 2 | No grade lines* | 1/4–3/4 in | 55 | 57 | 74 |
|---|---|---|---|---|---|
| SAE Grade 2 | No grade lines* | Over 3/4–1-1/2 in | 33 | 36 | 60 |
| SAE Grade 5 | 3 radial lines | 1/4–1 in | 85 | 92 | 120 |
| SAE Grade 5 | 3 radial lines | Over 1–1-1/2 in | 74 | 81 | 105 |
| SAE Grade 8 | 6 radial lines | 1/4–1-1/2 in | 120 | 130 | 150 |
*The Grade 2 small-diameter values apply to bolts 6 in long or shorter and to studs (consult SAE J429 for the full exception). Longer bolts may fall under Grade 1 requirements. Do not classify an unknown unmarked bolt as Grade 2.
Bolt Grade Chart | Turn2Engineering | SAE/ISO/ASTM reference minimum stresses. Confirm specifications and limitations.
Metric · ISO 898-1
Metric Bolt Grade Chart: 8.8, 10.9 & 12.9
Metric bolt heads usually show their property class, such as 8.8, 10.9 or 12.9. These are not SAE grades or diameter designations. The values are minimum proof, yield and tensile stresses in MPa; exact applicability varies with product, size and thread pitch.
Swipe across to see proof, yield and tensile values →
| Class | Nominal diameter band | Proof (MPa) | Yield (MPa) | Tensile (MPa) |
|---|---|---|---|---|
| 8.8 | M1.6–M16, applicable sizes | 580 | 640 | 800 |
| 8.8 | Over M16–M39, applicable sizes | 600 | 660 | 830 |
| 10.9 | M5–M39, applicable sizes | 830 | 940 | 1,040 |
| 12.9 | M1.6–M39, applicable sizes | 970 | 1,100 | 1,220 |
Class 8.8 has separate published properties at up to M16 and above M16. The property-class notation describes nominal strength relationships; the ISO acceptance minima can differ from that shorthand. See ISO 898-1 and data sources.
Its nominal tensile basis is 800 MPa, and the second digit indicates a nominal yield-to-tensile ratio of 0.8. Always use the standard’s actual minimum values for engineering checks.
No. The strength levels are similar, but the thread systems, dimensions, material and installation requirements are not automatically interchangeable.
Show additional metric property classes (4.6–9.8)
| Class | Nominal tensile basis | Nominal yield ratio |
|---|---|---|
| 4.6 | 400 MPa | 0.6 |
| 4.8 | 400 MPa | 0.8 |
| 5.6 | 500 MPa | 0.6 |
| 5.8 | 500 MPa | 0.8 |
| 6.8 | 600 MPa | 0.8 |
| 9.8 | 900 MPa | 0.8 |
SAE vs. Metric Bolt Grades: Strength Comparison
Commonly compared on tensile strength: 120 ksi ≈ 827 MPa, while class 8.8 is 800 or 830 MPa minimum by size range.
Commonly compared on tensile strength: 150 ksi ≈ 1,034 MPa, while class 10.9 is 1,040 MPa minimum.
Not a substitution table. Do not swap SAE, metric, ASTM or stainless bolts based only on similar strength. Match thread, dimensions, grade, coating, temperature, mating nut/washer and the drawing or OEM specification.
ASTM Structural Bolt Grades: A325, A490 & F3125
Today, legacy A325/A490 designations are grades within ASTM F3125/F3125M, not current standalone ASTM specifications. Structural connections have their own material, bolting assembly and installation requirements.
| Grade | Typical style | Min tensile |
|---|---|---|
| A325 | Heavy hex | 120 ksi |
| F1852 | Twist-off / TC | 120 ksi |
| 144 | Heavy hex or twist-off | 144 ksi |
| A490 | Heavy hex | 150 ksi |
| F2280 | Twist-off / TC | 150 ksi |
ASTM F3125/F3125M-26 lists the consolidated structural bolt families and the additional 144 ksi grade. Values are not SAE J429 equivalence labels; refer to the applicable structural joint specification. Source.
ASTM F1554 Anchor Bolt Grades
Grades 36, 55 and 105 are anchor-rod designations based on specified minimum yield strengths, not SAE head-line codes.
| Grade | Diameter range | Min yield (ksi) | Tensile range (ksi) |
|---|---|---|---|
| Grade 36 | 1/2–4 in | 36 | 58–80 |
| Grade 55 | 1/2–4 in | 55 | 75–95 |
| Grade 105 | 1/2–3 in | 105 | 125–150 |
F1554 Grade 55 has special weldability considerations; do not assume an anchor rod is weldable from its grade label. Design and inspection of foundation anchorage require the applicable project documents.
Other Bolt Markings: ASTM A307 & Stainless
General-purpose carbon-steel bolts are commonly associated with 60 ksi minimum tensile strength. ASTM A307 is its own specification—not SAE Grade 2.
These are stainless material or material-plus-property-class identifications, not equivalents to Grade 5 or 8. Verify the relevant ASTM F593 or ISO 3506 specification.
Color, plating and magnetic response cannot establish bolt grade or strength. Manufacturer identification or traceability may be required even when the marking resembles a familiar illustration.
How to Identify an Unknown Bolt Safely
- Read the complete head: count true SAE radial grade lines; note numeric class, letter code and maker’s ID.
- Measure the shank/thread diameter: it is not the wrench size across the head.
- Measure thread pitch: distinguish UNC/UNF and metric pitches; threads may look deceptively similar.
- Confirm the full specification: material, heat treatment, coating, length, nut and washer and application.
- Check original design or OEM requirements: do not select tightening torque or safe load from head marking alone.
A head with three lines can also appear on other specification families such as ASTM A449. Markings are a useful starting point, not complete proof of compliance.
Proof Load vs. Yield vs. Tensile Strength
Specified stress that the fastener withstands in the proof-load test without unacceptable permanent set.
Minimum stress associated with a defined onset of permanent deformation.
Minimum ultimate tensile stress measured under the prescribed test method—not an allowable design load.
Strength values are stresses. Bolt capacity also depends on tensile stress area, thread engagement, connection geometry, fatigue, temperature, friction and loading direction. Obtain installation torque from the product or joint specification—not a simple grade lookup.
Bolt Grade Chart FAQ
What do 3 lines and 6 lines on a bolt head mean?
On common SAE J429 fasteners, 3 radial grade lines indicate Grade 5 and 6 radial lines indicate Grade 8. Manufacturer logos are not extra grade lines. Some other standards may use similar markings.
What grade is a bolt with no markings?
Unknown. SAE Grade 2 fasteners commonly lack radial grade lines, but absence of markings cannot establish grade or material. Confirm the procurement specification or traceable identification.
Is Grade 8 stronger than Grade 5?
In the common SAE size bands, Grade 8 has a 150 ksi minimum tensile stress versus 120 ksi for Grade 5: 25% higher tensile minimum. This does not mean the entire joint has 25% more allowable capacity.
What does 8.8 on a metric bolt head mean?
It is an ISO metric property class. The designation encodes nominal tensile strength and a nominal yield ratio, but actual ISO minimum requirements have size-based bands for class 8.8.
Is a metric 10.9 bolt the same as SAE Grade 8?
No. Minimum tensile stress values are close, but geometry, pitch, coatings, fastener specifications and replacement requirements are not equivalent.
Do bolt grades determine torque?
No. Tightening torque requires the actual fastener and joint specification, including nominal diameter, thread, friction and target preload. Do not infer it solely from grade.
Are A325 and A490 still bolt grades?
Yes. They are now structural fastener grade designations in ASTM F3125/F3125M, not standalone current specifications. Their installation requirements are not SAE Grade 5/8 rules.
What does Grade 55 mean on an anchor bolt?
ASTM F1554 Grade 55 identifies a 55 ksi minimum yield-strength anchor rod category. It does not imply a particular tightening torque.
Standards & Engineering Data Sources
Checked October 2026. These tables are concise reference summaries, not a replacement for purchased standards or engineering design verification. Units converted in the finder are arithmetic conversions, not new specification values.
- Portland Bolt — SAE J429 specification summary (diameter bands, proof/yield/tensile minima and Grade 2 length qualification).
- SAE J429 — mechanical and material requirements for externally threaded fasteners (governing US inch-series standard).
- ISO 898-1:2013 (current published edition, confirmed in 2025; mechanical-property classes, thread and size applicability).
- The Fastener App — metric property class data (published reference values and size bands).
- ASTM F3125/F3125M-26 (A325, A490, F1852, F2280 and 144 ksi families).
- Portland Bolt — ASTM F1554 anchor-bolt grades (Grades 36, 55 and 105).