Nut & Bolt Grade Compatibility
The nut has to be as strong as the bolt — or the threads strip before the bolt ever does its job. Here’s which nut goes with which grade.
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.
The one rule that matters
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.
The common pairs at a glance
Heavy hex structural nuts carry their grade letters on the face. Full list, including stainless, in the table below.
| 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. |
A couple of things worth knowing
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.