Scope
SAE J429 covers the mechanical and material requirements for externally threaded inch-series fasteners used in general automotive and industrial applications. It defines strength grades by tensile, yield, and hardness for bolts, studs, and screws.
J429 is the SAE equivalent of the ASTM A307/A449/A354 family, and grades overlap functionally:
- SAE Grade 2 ≈ ASTM A307 Grade A (low carbon, general purpose)
- SAE Grade 5 ≈ ASTM A449 (medium-strength Q&T, similar strength up to 1")
- SAE Grade 8 ≈ ASTM A354 BD (high-strength alloy Q&T at 150 ksi)
Drawings citing SAE J429 grades are the industrial default; ASTM equivalents are generally acceptable substitutions when no specific SAE callout is mandated.
Grades and head markings
The visual grade-identification system on SAE bolt heads is one of the few things that makes fastener identification easy at a glance:
| Grade | Head markings | Material |
|---|---|---|
| Grade 1 | No radial lines | Low carbon steel (rarely specified new) |
| Grade 2 | No radial lines | Low or medium carbon steel |
| Grade 5 | 3 radial lines (120° spacing) | Medium carbon, Q&T |
| Grade 5.2 | 3 radial lines | Low-carbon martensitic |
| Grade 7 | 5 radial lines | Medium-carbon alloy, Q&T and roll-threaded |
| Grade 8 | 6 radial lines | Medium-carbon alloy, Q&T |
| Grade 8.2 | 6 radial lines | Low-carbon boron, Q&T |
Grade 5 and Grade 8 are the dominant commercial grades. Other grades see limited use.
Mechanical properties — common grades
Grade 2
| Diameter | Min. Tensile | Min. Yield | Min. Proof Load | Hardness |
|---|---|---|---|---|
| 1/4" through 3/4" | 74 ksi | 57 ksi | 55 ksi | B70–B100 HRB |
| Over 3/4" through 1-1/2" | 60 ksi | 36 ksi | 33 ksi | B70–B100 HRB |
Note that Grade 2 drops significantly above 3/4" — similar phenomenon to A449 but even more pronounced.
Grade 5
| Diameter | Min. Tensile | Min. Yield | Min. Proof Load | Hardness |
|---|---|---|---|---|
| 1/4" through 1" | 120 ksi | 92 ksi | 85 ksi | C25–C34 HRC |
| Over 1" through 1-1/2" | 105 ksi | 81 ksi | 74 ksi | C19–C30 HRC |
Grade 8
| Diameter | Min. Tensile | Min. Yield | Min. Proof Load | Hardness |
|---|---|---|---|---|
| 1/4" through 1-1/2" | 150 ksi | 130 ksi | 120 ksi | C33–C39 HRC |
Grade 8 maintains 150 ksi across the full size range — no diameter drop.
Chemistry
- Grade 2: Low-to-medium carbon steel, no alloy content required
- Grade 5: Medium carbon steel (0.28–0.55% C), Q&T; may contain boron additions
- Grade 8: Medium carbon alloy steel, with alloying from Cr, Ni, Mo, or V; Q&T to higher hardness than Grade 5
Grade 5 vs Grade 8 — the common decision
Probably the most frequent fastener-selection question in North American industrial practice:
| Factor | Grade 5 | Grade 8 |
|---|---|---|
| Tensile | 120 ksi | 150 ksi |
| Cost | Baseline | ~25–40% higher |
| Ductility | Higher | Lower |
| Notch sensitivity | Lower | Higher |
| Corrosion resistance | Similar (both plain carbon steel; requires coating) | Similar |
| When to upgrade | Need higher clamping force or lower weight for same load | Same |
| When NOT to upgrade | Cyclic or impact loading; marginal lubrication | — |
Grade 8 is not always the right answer. In cyclic loading, the higher hardness of Grade 8 makes it more notch-sensitive and sometimes less fatigue-tolerant than a Grade 5 bolt at the same installed tension. For static loading, Grade 8 gives more safety margin per bolt.
Recommended nuts and washers
| Bolt | Nut | Washer |
|---|---|---|
| Grade 2 | SAE J995 Grade 2 | F844 plain |
| Grade 5 | SAE J995 Grade 5, ASTM A563 Grade A or DH | F844 standard; F436 if tensioned |
| Grade 8 | SAE J995 Grade 8, ASTM A563 Grade DH | F436 hardened |
Nuts are graded similarly to bolts — matching grade ensures the joint fails the bolt in tension, not the nut in stripping.
Applications
- Automotive assembly (engine, chassis, driveline, suspension)
- OEM industrial equipment
- Agricultural and construction equipment
- Heavy machinery
- Trailer and transportation hardware
- General manufacturing
- HVAC and appliance manufacturing
Marking
Bolt heads carry the radial-line count identifying the grade, plus the manufacturer's identification symbol. Grade is readable at a glance by counting lines — the one visual system anyone can learn in 30 seconds.
Related specifications
- SAE J995 — Nuts (matching grades)
- ASTM A307 — Grade 2 equivalent
- ASTM A449 — Grade 5 equivalent (up to 1")
- ASTM A354 Grade BD — Grade 8 equivalent
- ASTM A574 — Alloy socket-head cap screws (often specified when higher strength + compact head are needed)
- F844 / F436 — Washers
- F1941 — Zinc electroplating
- F2329 — Hot-dip galvanizing
Documentation
California Fastener SAE J429 orders ship with mill certificates showing grade, heat number, chemistry, mechanical properties (tensile, yield, proof load, hardness), and finish. ISO 9001 traceability applies throughout.