Scope
SAE J995 covers the mechanical and material requirements for steel nuts used with J429 bolts, screws, and studs. It defines proof-load testing, hardness, and material requirements for regular hex, heavy hex, and hex flange nuts in inch-series sizes.
J995 is the SAE equivalent of ASTM A563, and grades overlap functionally:
- SAE Grade 2 ≈ ASTM A563 Grade A
- SAE Grade 5 ≈ ASTM A563 Grade A or B (depending on size)
- SAE Grade 8 ≈ ASTM A563 Grade DH
Grades and head markings
Like J429 bolts, J995 nuts use dots, dashes, and numerals to identify grade at a glance:
| Grade | Typical markings | Material |
|---|---|---|
| Grade 2 | No markings required | Low or medium carbon steel |
| Grade 5 | 3 dots (at 120° around the face), or "5" numeral | Medium carbon, Q&T |
| Grade 8 | 6 dots, or "8" numeral | Medium carbon alloy, Q&T |
Grade 8 is sometimes marked with a single dot surrounded by clock-marks (a pattern of radial notches) as an alternative visual system.
Mechanical properties — proof load stress
J995 grades are tested by proof load — the tensile force the nut must resist without stripping:
| Grade | Proof Load Stress (up to 1") | Proof Load Stress (over 1") |
|---|---|---|
| Grade 2 | 55 ksi | 33 ksi |
| Grade 5 | 120 ksi | 105 ksi |
| Grade 8 | 150 ksi | 150 ksi |
The nut proof load is set to exceed the bolt tensile capacity — a properly matched grade-on-grade assembly will break the bolt before stripping the nut.
Hardness requirements
| Grade | Hardness range |
|---|---|
| Grade 2 | 89 HRB max |
| Grade 5 | C19 to C32 HRC (or B89 to C32 HRC for smaller sizes) |
| Grade 8 | C24 to C38 HRC |
Matching grade is not optional
The single most important rule for any graded bolt/nut system: the nut grade must match or exceed the bolt grade. Common failure mode: a Grade 5 nut installed on a Grade 8 bolt. The bolt is strong; the nut is not. At design load, the nut threads strip, the bolt drops out of the joint, and the connection fails.
Visual identification prevents this — if you see 6 dots on the bolt, you want to see 6 dots (or "8") on the nut.
Hex vs heavy hex
J995 covers both regular hex nuts and heavy hex nuts. For Grade 5 and Grade 8 assemblies:
- Regular hex is adequate for most automotive and OEM service where the full proof-load test has been performed
- Heavy hex is preferred for structural, high-vibration, or critical applications — the extra wall thickness provides more thread engagement margin
For structural connections (AISC / RCSC work), heavy hex is required — but those connections are generally spec'd to ASTM A563, not SAE J995.
Applications
- Automotive assembly
- Industrial equipment
- Agricultural and construction machinery
- Trailer and transportation hardware
- OEM manufacturing
- General-purpose bolted assembly
Related specifications
- SAE J429 — Bolts (pair within grade)
- ASTM A563 — Structural/industrial nut alternative
- ASTM A194 — High-temp/pressure nuts (when service demands it)
- F844 — Plain flat washers
- F436 — Hardened washers (typically with Grade 8 pretensioned connections)
Documentation
California Fastener SAE J995 orders ship with mill certificates showing grade, heat number, proof-load test results, and hardness.