FASTENER REFERENCE
Fastener Torque Chart
SAE and metric bolt torque specs in ft-lbs and N·m. Compare Grade 2/5/8, Class 8.8/10.9/12.9, and stainless steel values with dry and lubricated data.
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SAE Grade 2/5/8
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Metric 8.8/10.9/12.9
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Dry & Lubricated Values
Fastener Torque
Key parameters at a glance
GradeSAE J429 / ISO 898-1
ThreadUNC / UNF / Metric Coarse
ConditionDry vs. Lubricated
Unitsft-lbs / N·m
Torque Reference
T = K × D × P
FASTENER ENGINEERING
What Is Fastener Torque?
Fastener torque is the rotational force applied to a bolt or nut during tightening, measured in foot-pounds (ft-lbs) or Newton-meters (N·m).
Torque does not directly clamp the joint. It overcomes thread and under-head friction so the bolt can stretch elastically — and that stretch is what generates clamp load. Too little clamp load and the joint works loose under vibration. Too much and the bolt yields, permanently losing tension.
Torque-Tension Equation
T = K × D × P. K is the nut factor (friction coefficient), D is bolt diameter, P is desired preload. K changes with lubrication: dry steel ≈ 0.20, oiled ≈ 0.15, anti-seize ≈ 0.12.
Grade & Class Matter
SAE Grade 5 has 3 radial lines on the head; Grade 8 has 6. Metric 8.8 and 10.9 are stamped on the head. Applying a Grade 8 torque value to a Grade 2 bolt will snap it.
Lubrication Reduces Torque
Applying dry-thread torque values to an oiled bolt is the most common cause of snapped fasteners. Lubrication reduces required torque by 20–35%.
TORQUE REFERENCE DATA
Fastener Torque Chart: SAE & Metric Bolt Torque Specs
SAE Grade 2/5/8 and Metric Class 8.8/10.9/12.9 torque values in ft-lbs and N·m — dry and lubricated.
Note: Torque values are general reference recommendations per SAE J429 and ISO 898-1. Values assume clean, undamaged threads at room temperature. Always defer to equipment manufacturer specifications for safety-critical joints.
SAE Grade 2, 5 & 8 — UNC / UNF
Inch-series fastener torque chart. UNF (fine thread) typically requires 5–10% higher torque than UNC at the same diameter and grade.
| Bolt Size | Thread | Wrench | Gr.2 Dry | Gr.2 Lubed | Gr.5 Dry | Gr.5 Lubed | Gr.8 Dry | Gr.8 Lubed | Clamp Load (lbs) Gr.8 |
|---|---|---|---|---|---|---|---|---|---|
| 1/4″ | 20 UNC / 28 UNF | 7/16″ | 4 | 3 | 8 | 6 | 12 | 9 | 2,850 |
| 5/16″ | 18 UNC / 24 UNF | 1/2″ | 8 | 6 | 17 | 13 | 24 | 18 | 4,720 |
| 3/8″ | 16 UNC / 24 UNF | 9/16″ | 15 | 11 | 31 | 23 | 44 | 33 | 7,020 |
| 7/16″ | 14 UNC / 20 UNF | 5/8″ | 24 | 18 | 49 | 37 | 70 | 52 | 9,900 |
| 1/2″ | 13 UNC / 20 UNF | 3/4″ | 37 | 28 | 75 | 57 | 105 | 80 | 13,550 |
| 9/16″ | 12 UNC / 18 UNF | 13/16″ | 53 | 40 | 110 | 82 | 155 | 115 | 17,550 |
| 5/8″ | 11 UNC / 18 UNF | 15/16″ | 73 | 55 | 150 | 113 | 210 | 158 | 22,400 |
| 3/4″ | 10 UNC / 16 UNF | 1-1/8″ | 125 | 94 | 270 | 200 | 380 | 285 | 33,900 |
| 7/8″ | 9 UNC / 14 UNF | 1-5/16″ | 190 | 143 | 420 | 315 | 600 | 450 | 47,800 |
| 1″ | 8 UNC / 14 UNF | 1-1/2″ | 285 | 214 | 650 | 483 | 820 | 615 | 64,000 |
| 1-1/8″ | 7 UNC / 12 UNF | 1-11/16″ | 404 | 303 | 900 | 672 | 1,200 | 900 | 82,800 |
| 1-1/4″ | 7 UNC / 12 UNF | 1-7/8″ | 566 | 425 | 1,260 | 945 | 1,680 | 1,260 | 104,500 |
Metric Class 8.8, 10.9 & 12.9 — Coarse Pitch
Metric fastener torque chart per ISO 898-1. For fine-pitch threads (e.g., M10×1.25), increase coarse-pitch torque by 8–12%.
| Bolt Size | Pitch (mm) | Wrench | 8.8 Dry (N·m / ft-lbs) | 8.8 Lubed (N·m / ft-lbs) | 10.9 Dry (N·m / ft-lbs) | 10.9 Lubed (N·m / ft-lbs) | 12.9 Dry (N·m / ft-lbs) | Clamp Load (kN) Cl.10.9 |
|---|---|---|---|---|---|---|---|---|
| M5 | 0.8 | 8 | 6.2 / 4.6 | 4.7 / 3.5 | 8.8 / 6.5 | 6.6 / 4.9 | 10.4 / 7.7 | 5.8 |
| M6 | 1.0 | 10 | 10.5 / 7.7 | 7.9 / 5.8 | 15 / 11 | 11 / 8.1 | 17.5 / 12.9 | 9.8 |
| M8 | 1.25 | 13 | 25 / 18.4 | 19 / 14 | 36 / 26.5 | 27 / 19.9 | 42 / 31 | 18.2 |
| M10 | 1.5 | 16 | 50 / 37 | 38 / 28 | 71 / 52 | 53 / 39 | 83 / 61 | 29.2 |
| M12 | 1.75 | 18 | 87 / 64 | 65 / 48 | 123 / 91 | 92 / 68 | 144 / 106 | 42.6 |
| M14 | 2.0 | 21 | 138 / 102 | 104 / 77 | 196 / 145 | 147 / 108 | 229 / 169 | 59.0 |
| M16 | 2.0 | 24 | 215 / 158 | 161 / 119 | 302 / 223 | 227 / 167 | 354 / 261 | 81.6 |
| M18 | 2.5 | 27 | 295 / 217 | 221 / 163 | 421 / 310 | 316 / 233 | 492 / 363 | 100 |
| M20 | 2.5 | 30 | 413 / 304 | 310 / 228 | 587 / 433 | 440 / 324 | 688 / 507 | 127 |
| M24 | 3.0 | 36 | 715 / 527 | 536 / 395 | 1,016 / 749 | 762 / 562 | 1,189 / 877 | 183 |
| M30 | 3.5 | 46 | 1,418 / 1,046 | 1,064 / 785 | 2,016 / 1,487 | 1,512 / 1,115 | 2,361 / 1,741 | 291 |
Stainless Steel — A2-70 & A4-80
Stainless fasteners require anti-seize. Values below assume anti-seize applied. For dry stainless threads, increase by 15–25% but expect significant galling risk.
| Bolt Size | Thread | A2-70 (ft-lbs / N·m) | A4-80 (ft-lbs / N·m) | Clamp Load (lbs) A2-70 |
|---|---|---|---|---|
| 1/4″ | 20 UNC / 28 UNF | 6.3 / 8.5 | 7.5 / 10.2 | 1,200 |
| 5/16″ | 18 UNC / 24 UNF | 11 / 15 | 13 / 17.6 | 2,030 |
| 3/8″ | 16 UNC / 24 UNF | 20 / 27 | 24 / 32.5 | 3,150 |
| 7/16″ | 14 UNC / 20 UNF | 32 / 43 | 38 / 51.5 | 4,420 |
| 1/2″ | 13 UNC / 20 UNF | 43 / 58 | 51 / 69 | 5,880 |
| 9/16″ | 12 UNC / 18 UNF | 62 / 84 | 74 / 100 | 7,600 |
| 5/8″ | 11 UNC / 18 UNF | 93 / 126 | 111 / 150 | 9,800 |
| 3/4″ | 10 UNC / 16 UNF | 152 / 206 | 181 / 245 | 14,700 |
| 7/8″ | 9 UNC / 14 UNF | 245 / 332 | 293 / 397 | 20,700 |
| 1″ | 8 UNC / 14 UNF | 358 / 485 | 428 / 580 | 27,800 |
SAE J429 & ISO 898-1
Torque values follow SAE and ISO fastener standards for carbon, alloy, and stainless steel bolts. Always verify against the latest standard edition.
Head Markings
Grade 5 = 3 radial lines. Grade 8 = 6 radial lines. Metric 8.8 and 10.9 stamped on head. Unmarked heads are Grade 2 (low strength).
READING GUIDE
How to Read This Fastener Torque Chart
Find your bolt size, identify the grade from head markings, match thread condition, and read the torque value.
01
Find the Bolt Size
Locate your bolt diameter in the leftmost column. For metric, note the pitch (coarse vs fine).
02
Identify the Grade
Check the head marking: SAE Grade 5 = 3 lines, Grade 8 = 6 lines. Metric 8.8, 10.9, 12.9 stamped on head.
03
Choose Thread Condition
Match the column to actual assembly condition — dry or lubricated. Using the wrong column snaps fasteners.
Bolt Grade & Strength Class Reference
| Grade / Class | Head Marking | Standard | Tensile (ksi / MPa) | Proof (ksi / MPa) | Typical Use |
|---|---|---|---|---|---|
| SAE Grade 2 | No marks | SAE J429 | 74 / 510 | 55 / 379 | Light-duty hardware, general non-structural |
| SAE Grade 5 | 3 radial lines | SAE J429 | 120 / 827 | 85 / 586 | Standard automotive, machinery |
| SAE Grade 8 | 6 radial lines | SAE J429 | 150 / 1,034 | 120 / 827 | Suspension, drivetrain, high-stress |
| Class 8.8 | Stamped “8.8” | ISO 898-1 | 116 / 800 | 84 / 580 | General automotive (≈ Grade 5) |
| Class 10.9 | Stamped “10.9” | ISO 898-1 | 151 / 1,040 | 120 / 830 | High-stress structural (≈ Grade 8) |
| Class 12.9 | Stamped “12.9” | ISO 898-1 | 177 / 1,220 | 141 / 970 | Racing, tooling, socket head cap screws |
| A2-70 (304) | Stamped “A2-70” | ISO 3506 | 102 / 700 | 65 / 450 | General stainless, corrosion-resistant |
| A4-80 (316) | Stamped “A4-80” | ISO 3506 | 116 / 800 | 87 / 600 | Marine-grade, high-corrosion |
Example: 1/2″-13 Grade 5 Bolt
A 1/2″-13 Grade 5 bolt (3 radial lines) with dry threads needs 75 ft-lbs. The same bolt oiled needs 57 ft-lbs. Applying the dry value to an oiled bolt over-tightens by 32% — enough to yield the bolt or strip aluminum threads.
75 ft-lbsDry — use for clean bare steel
57 ft-lbsLubricated — use for oiled/plated
33%Torque reduction needed
Dry vs. Lubricated Torque — The K-Factor
Lubrication reduces friction, and reduced friction means more of the wrench torque goes into stretching the bolt rather than overcoming thread resistance. Applying dry-thread torque values to lubricated threads is the most common cause of snapped fasteners.
| Thread Condition | Approximate K-Factor | Torque Multiplier vs. Dry | What It Means |
|---|---|---|---|
| Dry steel (bare, clean) | 0.20 | 1.00 (reference) | Baseline; maximum friction |
| Zinc plated / galvanized | 0.18 | 0.85–0.90 | Plating acts as a mild solid lubricant |
| Light machine oil | 0.15 | 0.75–0.80 | The most common assembly condition |
| Anti-seize (copper or moly) | 0.12 | 0.60–0.75 | Maximum lubricity; largest torque reduction |
| Hot-dip galvanized (HDG) | 0.25 | 1.20–1.25 | Rough coating increases friction |
The golden rule: If the bolt manufacturer or equipment OEM specifies a torque value but does not state dry or lubricated, assume dry unless the fastener comes pre-coated with oil or plating. Most black-oxide and plain-finish bolts ship with a light oil film for corrosion protection, which puts them in the “light machine oil” category. When in doubt, measure — torque a sample bolt and verify clamp load with a load cell for critical joints.
BEST PRACTICES
Torque Tightening Best Practices
A correct torque value from this chart is the starting point. How you apply it determines whether the joint actually achieves the target clamp load.
Torque is the input you measure with a wrench; clamp load is the output that holds the joint together. Friction changes with lubrication, plating, and thread condition — and torque values must follow.
Staged Tightening
Tighten in Stages
Three stages: 30% of target torque, then 70%, then 100%. Tighten in a cross pattern (star) for circular bolt patterns, or from center outward for rectangular patterns. Prevents uneven compression.
Wrench Accuracy
Use the Right Wrench
Target torque should fall in the middle third of the wrench’s range. Recalibrate annually. Calibration drift is a common root cause of under- and over-torque failures.
Torque-to-Yield
TTY = One-Time-Use
TTY bolts (cylinder heads, connecting rods) are tightened into plastic deformation. They are one-time-use — once removed, they must be replaced. Always follow angle-based OEM procedures.
What Happens When You Get It Wrong
Over-torque: The bolt yields (permanently stretches), threads strip in the mating part, gaskets crush unevenly, flanges warp. Under-torque: The joint lacks clamp load, the bolt self-loosens under vibration, fretting wear develops, fatigue failure follows. Both are preventable with a calibrated torque wrench and the correct column from the chart above.
Over-TorqueYields bolt, strips threads
Under-TorqueSelf-loosens, fatigue failure
CorrectLong joint life
Fastener Torque FAQs
Frequently Asked Questions
The correct torque depends on four things: bolt diameter, thread pitch, material grade (head marking), and whether threads are dry or lubricated. Find your bolt size in the left column of the chart, match the grade to the head marking, then choose the dry or lubricated column based on actual thread condition. A 1/2″-13 Grade 5 bolt with dry threads needs 75 ft-lbs; the same bolt oiled needs 57 ft-lbs.
Grade 5 bolts (3 radial lines) have 120,000 psi tensile strength. Grade 8 bolts (6 radial lines) have 150,000 psi tensile strength, roughly 25% stronger. Grade 8 bolts accept roughly 40% more torque than Grade 5 bolts of the same size. Grade 5 is standard automotive/machinery; Grade 8 is used for suspension, drivetrain, and high-stress structural joints.
Metric Class 8.8 is roughly equivalent to SAE Grade 5 (800 MPa tensile). Class 10.9 is roughly equivalent to SAE Grade 8 (1,040 MPa tensile). “8.8” = 800 MPa tensile and 80% yield ratio. “10.9” = 1,000 MPa tensile and 90% yield ratio. The chart provides separate torque columns for each class because torque values differ by roughly 40%.
Yes, by 20–35% depending on lubricant. Applying the dry-thread torque value to an oiled bolt is the single most common cause of snapped fasteners. Use the lubricated torque column in the chart, or reduce the dry value by 25% for oiled threads and 35% for anti-seize.
Use stainless-specific torque values, not carbon steel values. The stainless steel table provides separate values for A2-70 (304) and A4-80 (316) with anti-seize applied. Anti-seize is mandatory for stainless fasteners — stainless-on-stainless threads gall (cold-weld) under pressure. For food-contact or high-vacuum applications that cannot tolerate anti-seize, use different materials for the bolt and tapped component.
Clamp load (preload) is the tension force in the bolt shank that squeezes the joint together. It is the actual engineering output of tightening. A bolted joint works because clamp load creates friction between joint faces that prevents slip. If too low, the joint slips and the bolt fails from fatigue. If too high, the bolt yields or joint components crush. The clamp load columns in the torque charts show the resulting preload for the recommended torque values.
Use the column that matches the actual condition of your threads at assembly. Clean, bare steel = dry values. Threads with light oil (most factory bolts) = lubricated values. Zinc-plated = reduce by 10–15%. Anti-seize = reduce by 25–40%. The most common mistake is assuming factory-fresh bolts are dry — most black-oxide and plain-finish bolts ship with a light corrosion-prevention oil.
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