A bolt is only as strong as the nut on it. Pair a high-grade bolt with a soft nut and the nut threads strip out long before the bolt reaches its rated strength — a quiet, dangerous failure. The fix is simple: match the nut to the bolt grade (or go stronger). Here are the standard pairings.
Use a nut that is at least as strong as the bolt. Stronger is fine; weaker is not. When in doubt, step up — an over-strong nut never hurt a joint.
| Bolt grade | Use this nut | Notes |
|---|---|---|
| SAE Grade 2 | SAE Grade 2 hex nut, or ASTM A563 Grade A | General-purpose, low-strength work. |
| SAE Grade 5 | SAE Grade 5 hex nut, or ASTM A563 Grade A | The common shop pairing for Grade 5 bolts. |
| SAE Grade 8 | SAE Grade 8 hex nut, or ASTM A563 Grade DH | Don’t drop below Grade 8 here — the nut must keep up. |
| ASTM A307 | ASTM A563 Grade A hex nut | Low-strength structural / anchor bolts. |
| ASTM A325 | ASTM A563 DH or A194 Grade 2H heavy hex nut | Structural steel connections; nuts marked “DH” or “2H.” |
| ASTM A490 | ASTM A563 DH or A194 Grade 2H heavy hex nut | High-strength structural; same heavy nuts as A325. |
| 18-8 / 304 stainless | 18-8 (304) stainless nut | Match the alloy — corrosion resistance is the point. |
| 316 stainless | 316 stainless nut | For marine / chemical exposure; match 316 to 316. |
Stainless can gall. Stainless nuts and bolts run together can seize from friction (galling), especially if driven fast and dry. Slow it down and use an anti-seize on the threads — ask us which.
Not sure of the bolt grade? Read the head markings on the bolt grades & strength chart, then come back here for the matching nut. Or bring the bolt in and we’ll match the whole set — nut, washer, and grade.
