Nut grade pairing compared: lock, flange, jam and heavy hex nuts
A nut is specified backward from its bolt: the nut has to develop the bolt's full proof load, or the joint's failure mode moves from visible bolt fracture to gradual thread stripping. This table compares the six nut patterns we publish individual specification pages for — two prevailing-torque lock nuts, a serrated flange nut, a jam nut and the two heavy hex structural grades — using only fields that mean the same thing across the columns. Where a figure is not established by the collected evidence, the cell says so and asks you to confirm it at RFQ; nothing is filled in with an assumption.
Comparison table
All entries are minimums or stated conditions per the governing standard named in each column. Metric DIN patterns and inch-series structural grades are tabulated side by side for procurement orientation — a substitution between the two families should always be confirmed with the engineer of record (see the FAQ below).
| Field | DIN 985 Nylon-Insert Lock Nut | DIN 980 All-Metal (Stover) Lock Nut | DIN 6923 Serrated Flange Nut | DIN 439 Thin Jam Nut | ASME B18.2.2 Heavy Hex Nut | ASTM A194 Gr. 2H Heavy Hex Nut |
|---|---|---|---|---|---|---|
| Standard & pattern | DIN 985 — hex lock nut with nylon insert (non-metallic prevailing torque) | DIN 980 / DIN 6925 — all-metal prevailing-torque lock nut (Stover type) | DIN 6923 — serrated hex flange nut (inch counterparts IFI 100/107) | DIN 439 — thin hexagonal jam nut, thickness 0.5 × diameter (Type A/B) | ASME B18.2.2 — heavy hex nut, inch series, 1/4"–4" | ASTM A194 Grade 2H — heavy hex nut, 1/4"–4" |
| Anti-loosening mechanism How each nut resists back-off. Differs by design across the columns: prevailing torque (nylon or distorted thread), surface bite, or none built in. | Nylon collar deforms around the bolt threads and grips by friction | Distorted top thread grips the bolt by metal-to-metal friction — no insert | Differs in kind — flange teeth bite the bearing surface and resist back-off (no prevailing torque) | Differs in kind — threaded up against a standard nut to lock it in place; no locking of its own | None built in — the joint carries on preload and the matched nut grade | None built in — the joint carries on preload and the matched stud/bolt grade |
| Temperature capability Where the collected pages state a basis, it is quoted; where they are silent, the cell is unverified rather than assumed. | About 250°F (≈120°C) — above it the nylon softens and the lock degrades | High — all-steel construction, no polymer insert to soften (no hour/°C rating collected; confirm at RFQ) Conditional — confirm configuration | High — all-steel construction (no numeric rating collected; confirm at RFQ) Conditional — confirm configuration | Unverified — the collected page does not state a temperature limit; confirm at RFQ Unverified — confirm at RFQ | Unverified — grade-dependent (A563/A194 grades differ); confirm at RFQ Unverified — confirm at RFQ | Unverified — the collected page does not state a service temperature; confirm at RFQ Unverified — confirm at RFQ |
| Bolt / stud pairing The pairing rule behind the knowledge guide: the nut must develop the bolt's full proof load, so the nut grade moves with the bolt grade. | Match to the bolt grade — the collected page does not tabulate a class chart; confirm at RFQ Unverified — confirm at RFQ | Match to the bolt grade; Grade 9 all-metal version for Grade 8 / Grade 9 bolt assemblies | Use with a screw of comparable strength — serrated-flange inch counterpart is rated SAE Grade 5 Conditional — confirm configuration | Locker for a standard nut of matching thread — not the working nut of the joint | A325 Type 1: A563 C/C3/D/DH/DH3 or A194 2H; A490 Type 1: DH/DH3/2H; galvanized A325: DH or 2H | A193 B7 studs (default refinery/pipeline pairing); accepted with A325 Type 1 and A490 Type 1 |
| Reuse Same meaning across columns where stated; not all pages address it. | Reusable a few times before the nylon insert wears out | Good — tolerates more installation cycles than a nylon-insert nut | Unverified — the collected page does not address reuse cycles; confirm at RFQ Unverified — confirm at RFQ | Unverified — not addressed in the collected page; confirm at RFQ Unverified — confirm at RFQ | Unverified — not addressed in the collected page; confirm at RFQ Unverified — confirm at RFQ | Unverified — not addressed in the collected page; confirm at RFQ Unverified — confirm at RFQ |
| Proof-load / hardness basis Only where the collected page states a figure. A307-style "grade" names and metric classes are different measurement systems — see the knowledge guide for the pairing table. | Unverified — steel property classes per the mating bolt; not tabulated on the collected page Unverified — confirm at RFQ | Unverified — not tabulated on the collected page; confirm at RFQ Unverified — confirm at RFQ | Case hardened steel (commonly supplied condition; no proof-load figure collected) Conditional — confirm configuration | Unverified — not tabulated on the collected page; confirm at RFQ Unverified — confirm at RFQ | Grade-dependent: A563 grades run 69–175 ksi proof-load stress (O through DH/DH3) Conditional — confirm configuration | 175 ksi proof-load stress; C24–C38 Rockwell |
- Verified
- Differs
- Unverified — confirm at RFQ
- Conditional — confirm configuration
How to choose
By the anti-loosening duty
Prevailing-torque lock nuts hold by friction that survives partial loosening cycles: the nylon-insert type is the everyday choice but surrenders near 120 °C, while the all-metal Stover pattern grips metal-to-metal and takes heat and reassembly. Flange nuts are not prevailing-torque at all — their serrations resist back-off by biting the surface, which also means they mar it. A jam nut locks nothing by itself; it locks the working nut it is jammed against.
By the bolt they carry
Structural inch-series bolts specify their nut by name: A325 Type 1 pairs with A563 C/C3/D/DH/DH3 or A194 2H, A490 Type 1 with DH/DH3/2H, and galvanized A325 with DH or 2H — a heavy hex body chosen precisely because it can develop the bolt's proof load. On the metric side the class system does the same job numerically. When in doubt, order the nut standard the drawing names and let the grade chart confirm the pair.
By the bearing surface
Where the joint face is soft, thin or oversized, the bearing area decides: the flange nut carries its own washer function, while plain and heavy hex nuts rely on a separate washer — hardened (ASTM F436) in structural work. The full bearing-surface and pairing mechanics are in the nut pairing knowledge guide linked below.
Frequently asked questions
Can I mix a higher-strength bolt with a standard nut?
The nut must be able to develop the bolt's proof load, or the joint's failure mode moves from visible bolt fracture to gradual thread stripping. The property-class system pairs class-8 nuts with 8.8 bolts, class 10 with 10.9 and class 12 with 12.9; a higher-class nut may always substitute for a lower one. Upgrading the bolt alone — without upgrading the nut — is the classic pairing error.
Which lock nut survives engine-bay or exhaust heat?
Not the nylon-insert type: the nylon collar softens around 250°F (≈120°C) and the prevailing torque degrades with it. All-metal prevailing-torque nuts (DIN 980 Stover type) hold by distorted-thread friction with no polymer to soften, and serrated flange nuts are likewise all-steel. For exact temperature limits beyond the nylon threshold, confirm the specific configuration at RFQ.
Do these nuts replace washers?
Only the flange nut builds the bearing function in — its flange spreads the load like an integrated washer, at the cost of teeth that mar the mating surface. Heavy hex nuts rely on separate hardened washers (ASTM F436 in structural work). The other patterns in this table bear on the joint face directly, with a plain washer added where the surface is soft or the hole oversized.
Individual nut specification pages
Each pattern has its own page — dimensions, pairing details and RFQ guidance.
- DIN 985 Nylon-Insert Lock Nut
- DIN 980 All-Metal (Stover) Lock Nut
- DIN 6923 Serrated Flange Nut
- DIN 439 Thin Jam Nut
- ASME B18.2.2 Heavy Hex Nut
- ASTM A194 Gr. 2H Heavy Hex Nut
The full pairing mechanics and bearing-surface guidance: Nut grade pairing and bearing surface selection
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