Letter Symbol Convention
In ANSI Standards for metric nuts, letter symbols designating dimensional characteristics are in accord with ISO Standards, except that capital letters are used (for data processing convenience) instead of the lower case letters used in ISO Standards. When cross-referencing between ANSI and ISO documents, remember that ANSI's "S" equals ISO's "s," ANSI's "M" equals ISO's "m," and so on.
Metric Nut Tops and Bearing Surfaces
The geometry of a nut's top and bearing surface directly affects how it distributes clamping load, how it seats against the joint surface, and whether it requires a washer. These are not decorative features — they are functional design elements governed by specific rules.
Chamfer and Washer-Face Rules in the supplied reference and Size
| Nut Type | M16 and Smaller | M20 and Larger |
|---|---|---|
| Hex Nuts, Styles 1 & 2 | Double chamfered | Double chamfered OR washer-faced bearing surface with chamfered top (manufacturer's option) |
| Slotted Hex Nuts | Double chamfered | Double chamfered OR washer-faced bearing surface with chamfered top (manufacturer's option) |
| Hex Jam Nuts | Double chamfered | Double chamfered OR washer-faced bearing surface with chamfered top (manufacturer's option) |
| Heavy Hex Nuts | Optional either way in all sizes | Optional either way in all sizes |
| Hex Flange Nuts | Flange bearing surface + chamfered top | Flange bearing surface + chamfered top |
| Prevailing-Torque Hex Nuts | Chamfered bearing surface | Chamfered bearing surface |
| Prevailing-Torque Hex Flange Nuts | Flange bearing surface | Flange bearing surface |
Critical Bearing Face Details
- All types of metric nuts have the tapped hole countersunk on the bearing face
- Slotted hex nuts, hex flange nuts, and prevailing-torque types (both hex and hex flange) may also be countersunk on the top face
- The countersink on the bearing face prevents thread damage to mating surfaces during assembly and ensures the nut seats flat against the joint
the practitioner's lesson here: When she specified Style 1 nuts for her gearbox assemblies, she got double-chamfered M20 nuts. The Style 2 nuts she needed would have provided a washer-faced bearing surface with significantly more consistent load distribution on the aluminum housing — a critical difference that contributed to the joint relaxation under cyclic loading.
Materials and Mechanical Properties
This is where metric nut selection becomes genuinely consequential. Choose the wrong property class and you create a joint where the nut is the weakest link — thread stripping replaces controlled bolt yielding as the failure mode, and you lose all predictability in your joint behavior.
Property Class Assignments in the supplied reference
Nonheat-Treated Carbon Steel
| Nut Type | Property Class | Governing Standard |
|---|---|---|
| Hex Nuts, Style 1 | Class 5 | ASTM A563M |
| Slotted Hex Nuts | Class 5 | ASTM A563M |
| Hex Nuts, Style 2 | Class 9 | ASTM A563M |
| Hex Flange Nuts | Class 9 | ASTM A563M |
| Hex Jam Nuts | Class 04 | ASTM A563M |
| Heavy Hex Nuts (carbon and alloy steel) | Classes 5, 9, 8S, or 8S3 | ASTM A563M |
Heat-Treated Carbon Steel
| Nut Type | Property Class | Governing Standard |
|---|---|---|
| Hex Nuts, Style 1 | Class 10 | ASTM A563M |
| Slotted Hex Nuts | Class 10 | ASTM A563M |
| Hex Nuts, Style 2 | Class 12 | ASTM A563M |
| Hex Jam Nuts | Class 05 | ASTM A563M |
| Hex Flange Nuts | Classes 10 and 12 | ASTM A563M |
| Heavy Hex Nuts (carbon or alloy steel) | Classes 10S, 10S3, or 12 | ASTM A563M |
Prevailing-Torque Types
| Nut Type | Governing Standard |
|---|---|
| Prevailing-Torque Hex Nuts | ANSI B18.16.1M |
| Prevailing-Torque Hex Flange Nuts | ANSI B18.16.1M |
Non-Ferrous Materials
Metric nuts of stainless steel, brass, bronze, and aluminum alloys have properties as agreed upon by the manufacturer and purchaser. Properties of several grades of non-ferrous materials are covered in ASTM F467M.
The Bolt-Nut Matching Principle
The property class system exists to ensure that the nut is always at least as strong as the bolt it mates with. The numeric designation provides a direct indication of capability:
- Property Class 5 nuts are suitable for use with bolts up to approximately class 5.8
- Property Class 9 nuts handle bolts up to approximately class 9.8
- Property Class 10 nuts are rated for bolts up to class 10.9
- Property Class 12 nuts match the highest-strength class 12.9 bolts
Rule of Thumb: The nut property class number should always equal or exceed the first digit of the bolt property class designation. A class 10 nut for a class 10.9 bolt. A class 12 nut for a class 12.9 bolt. Never go lower.
Default Finish
Unless otherwise specified, metric nuts are furnished with a natural (unprocessed) finish, unplated or uncoated. If you need zinc plating, hot-dip galvanizing, or any protective coating, you must specify it in the designation.
Metric Hex Nuts — Styles 1 and 2
These are the workhorses of metric fastening. Style 1 is the standard-height nut for general-purpose applications. Style 2 is taller, providing greater thread engagement and higher proof load capacity for high-strength bolt applications.
Governing Standards:
- Style 1: ANSI/ASME B18.2.4.1M-1979 (R1995) — coordinated with ISO 4032
- Style 2: ANSI/ASME B18.2.4.2M-1979 (R1995) — coordinated with ISO 4033
Style 1 vs. Style 2 — The Critical Differences
| Feature | Style 1 | Style 2 |
|---|---|---|
| Nonheat-treated property class | Class 5 | Class 9 |
| Heat-treated property class | Class 10 | Class 12 |
| Nut thickness | Standard | Taller (more thread engagement) |
| Typical bolt pairing | Up to class 8.8 | Class 9.8 through 12.9 |
| Size range | M1.6 through M36 | M3 through M36 |
Complete Dimensional Table — Metric Hex Nuts, Style 1
ANSI/ASME B18.2.4.1M-1979 (R1995) — All dimensions in millimeters
| Nominal Size & Thread Pitch | Width Across Flats, S | Width Across Corners, E | Thickness, M | Bearing Face Dia., Dw (Min) | Washer Face Thickness, C |
|---|---|---|---|---|---|
| Max | Min | Max | Min | Max | |
| M1.6 × 0.35 | 3.20 | 3.02 | 3.70 | 3.41 | 1.30 |
| M2 × 0.4 | 4.00 | 3.82 | 4.62 | 4.32 | 1.60 |
| M2.5 × 0.45 | 5.00 | 4.82 | 5.77 | 5.45 | 2.00 |
| M3 × 0.5 | 5.50 | 5.32 | 6.35 | 6.01 | 2.40 |
| M3.5 × 0.6 | 6.00 | 5.82 | 6.93 | 6.58 | 2.80 |
| M4 × 0.7 | 7.00 | 6.78 | 8.08 | 7.66 | 3.20 |
| M5 × 0.8 | 8.00 | 7.78 | 9.24 | 8.79 | 4.70 |
| M6 × 1 | 10.00 | 9.78 | 11.55 | 11.05 | 5.20 |
| M8 × 1.25 | 13.00 | 12.73 | 15.01 | 14.38 | 6.80 |
| M10 × 1.5 ⚠️ (15mm)* | 15.00 | 14.73 | 17.32 | 16.64 | 9.10 |
| M10 × 1.5 (16mm) | 16.00 | 15.73 | 18.48 | 17.77 | 8.40 |
| M12 × 1.75 | 18.00 | 17.73 | 20.78 | 20.03 | 10.80 |
| M14 × 2 | 21.00 | 20.67 | 24.25 | 23.36 | 12.80 |
| M16 × 2 | 24.00 | 23.67 | 27.71 | 26.75 | 14.80 |
| M20 × 2.5 | 30.00 | 29.16 | 34.64 | 32.95 | 18.00 |
| M24 × 3 | 36.00 | 35.00 | 41.57 | 39.55 | 21.50 |
| M30 × 3.5 | 46.00 | 45.00 | 53.12 | 50.85 | 25.60 |
| M36 × 4 | 55.00 | 53.80 | 63.51 | 60.79 | 31.00 |
⚠️ The M10 size with 15 mm width across flats is not an ISO Standard. Unless specifically ordered, the M10 with 16 mm width across flats will be furnished.
Complete Dimensional Table — Metric Hex Nuts, Style 2
ANSI/ASME B18.2.4.2M-1979 (R1995) — All dimensions in millimeters
| Nominal Size & Thread Pitch | Width Across Flats, S | Width Across Corners, E | Thickness, M | Bearing Face Dia., Dw (Min) | Washer Face Thickness, C |
|---|---|---|---|---|---|
| Max | Min | Max | Min | Max | |
| M3 × 0.5 | 5.50 | 5.32 | 6.35 | 6.01 | 2.90 |
| M3.5 × 0.6 | 6.00 | 5.82 | 6.93 | 6.58 | 3.30 |
| M4 × 0.7 | 7.00 | 6.78 | 8.08 | 7.66 | 3.80 |
| M5 × 0.8 | 8.00 | 7.78 | 9.24 | 8.79 | 5.10 |
| M6 × 1 | 10.00 | 9.78 | 11.55 | 11.05 | 5.70 |
| M8 × 1.25 | 13.00 | 12.73 | 15.01 | 14.38 | 7.50 |
| M10 × 1.5 ⚠️ (15mm)* | 15.00 | 14.73 | 17.32 | 16.64 | 10.00 |
| M10 × 1.5 (16mm) | 16.00 | 15.73 | 18.48 | 17.77 | 9.30 |
| M12 × 1.75 | 18.00 | 17.73 | 20.78 | 20.03 | 12.00 |
| M14 × 2 | 21.00 | 20.67 | 24.25 | 23.35 | 14.10 |
| M16 × 2 | 24.00 | 23.67 | 27.71 | 26.75 | 16.40 |
| M20 × 2.5 | 30.00 | 29.16 | 34.64 | 32.95 | 20.30 |
| M24 × 3 | 36.00 | 35.00 | 41.57 | 39.55 | 23.90 |
| M30 × 3.5 | 46.00 | 45.00 | 53.12 | 50.85 | 28.60 |
| M36 × 4 | 55.00 | 53.80 | 63.51 | 60.79 | 34.70 |
Style 1 vs. Style 2 Thickness Comparison
Notice the critical thickness differences — this is what gives Style 2 its superior proof load capacity:
| Size | Style 1 Thickness (Max) | Style 2 Thickness (Max) | Thickness Increase |
|---|---|---|---|
| M5 × 0.8 | 4.70 mm | 5.10 mm | +0.40 mm (8.5%) |
| M8 × 1.25 | 6.80 mm | 7.50 mm | +0.70 mm (10.3%) |
| M12 × 1.75 | 10.80 mm | 12.00 mm | +1.20 mm (11.1%) |
| M16 × 2 | 14.80 mm | 16.40 mm | +1.60 mm (10.8%) |
| M24 × 3 | 21.50 mm | 23.90 mm | +2.40 mm (11.2%) |
| M36 × 4 | 31.00 mm | 34.70 mm | +3.70 mm (11.9%) |
The roughly 10–12% increase in thickness translates to significantly more thread engagement. This additional engagement is what allows Style 2 nuts to achieve property class 9 (nonheat-treated) and class 12 (heat-treated) ratings, making them the correct choice for high-strength bolt applications.
Metric Slotted Hex Nuts
Slotted hex nuts incorporate a transverse slot across the top face that accepts a cotter pin or wire, providing a positive mechanical lock against rotation. They are specified wherever vibration loosening is a safety concern and the joint requires periodic disassembly — making castle-style locking impractical.
Governing Standard: ANSI B18.2.4.3M-1982 (R1999)
When to Specify Slotted Hex Nuts
- Safety-critical joints subject to vibration where positive locking is mandatory
- Applications requiring periodic inspection and disassembly (the cotter pin is removed, nut inspected, and reinstalled)
- Rotating shaft assemblies where a through-bolt and cotter pin secure the nut against axial loads
- Aircraft, automotive, and heavy equipment applications governed by maintenance standards requiring positive locking
Complete Dimensional Table — Metric Slotted Hex Nuts
ANSI B18.2.4.3M-1982 (R1999) — All dimensions in millimeters
| Nominal Size & Thread Pitch | Width Across Flats, S | Width Across Corners, E | Thickness, M | Bearing Face Dia., Dw (Min) | Unslotted Thickness, F | Width of Slot, N | Washer Face Thickness, C |
|---|---|---|---|---|---|---|---|
| Max | Min | Max | Min | Max | Min | ||
| M5 × 0.8 | 8.00 | 7.78 | 9.24 | 8.79 | 5.10 | 4.80 | 6.9 |
| M6 × 1 | 10.00 | 9.78 | 11.55 | 11.05 | 5.70 | 5.40 | 8.9 |
| M8 × 1.25 | 13.00 | 12.73 | 15.01 | 14.38 | 7.50 | 7.14 | 11.6 |
| M10 × 1.5 ⚠️ (15mm)* | 15.00 | 14.73 | 17.32 | 16.64 | 10.00 | 9.60 | 13.6 |
| M10 × 1.5 (16mm) | 16.00 | 15.73 | 18.48 | 17.77 | 9.30 | 8.94 | 14.6 |
| M12 × 1.75 | 18.00 | 17.73 | 20.78 | 20.03 | 12.00 | 11.57 | 16.6 |
| M14 × 2 | 21.00 | 20.67 | 24.25 | 23.35 | 14.10 | 13.40 | 19.6 |
| M16 × 2 | 24.00 | 23.67 | 27.71 | 26.75 | 16.40 | 15.70 | 22.5 |
| M20 × 2.5 | 30.00 | 29.16 | 34.64 | 32.95 | 20.30 | 19.00 | 27.7 |
| M24 × 3 | 36.00 | 35.00 | 41.57 | 39.55 | 23.90 | 22.60 | 33.2 |
| M30 × 3.5 | 46.00 | 45.00 | 53.12 | 50.85 | 28.60 | 27.30 | 42.7 |
| M36 × 4 | 55.00 | 53.80 | 63.51 | 60.79 | 34.70 | 33.10 | 51.1 |
Key Design Dimensions
- Unslotted Thickness (F): The solid portion below the slot. This must be sufficient to provide full thread engagement strength beneath the slot depth
- Width of Slot (N): Sized to accept standard cotter pins or safety wire. The slot width increases with nut size from 1.4 mm minimum at M5 to 7.0 mm minimum at M30 and M36
- Slot depth = Total thickness (M) minus Unslotted thickness (F). For example, an M16 slotted hex nut has a slot depth of approximately 16.40 − 9.90 = 6.50 mm
Metric Nut Thread Series
All metric nuts have metric coarse threads with class 6H tolerances in accordance with ANSI B1.13M. This is a universal standard that applies to every nut type covered in this guide.
Key Threading Rules
- For prevailing-torque type nuts, the class 6H tolerance condition applies before introduction of the prevailing torque feature. The torque-generating mechanism (distorted thread, nylon insert, etc.) is applied after the threads are cut to specification
- For plated or coated nuts — particularly those intended for use with externally threaded fasteners having a thick plating such as hot-dip galvanizing — the nut threads must be over-tapped to permit assembly. These over-tapped threads conform to requirements specified in ASTM A563M
- Thread pitch is inherent in the size designation. For example, M10 always implies M10 × 1.5 in the coarse thread series. ISO convention commonly omits the pitch from designations when the coarse series is used
The Over-Tapping Consideration
When you specify hot-dip galvanized bolts, the zinc coating adds material thickness to the external threads. The matching nuts must have their internal threads tapped oversize to accommodate this additional material. This is not a defect — it is a deliberately specified manufacturing process governed by ASTM A563M. However, it means:
- Galvanized nuts are not interchangeable with non-galvanized nuts on plain-finish bolts (the thread fit will be loose)
- Always order nuts and bolts in matching finish states to ensure proper thread engagement and load transfer
- Specify the coating in the nut designation so the manufacturer knows to apply the correct over-tapping procedure
Metric Hex Flange Nuts
Hex flange nuts incorporate an integral washer-like flange at the bearing surface that distributes clamping load over a larger area than a standard hex nut. This eliminates the need for a separate flat washer in many applications, reducing part count, assembly time, and the potential for washer-related assembly errors.
Governing Standard: ANSI B18.2.4.4M-1982 (R1999) — coordinated with ISO 4161
Complete Dimensional Table — Metric Hex Flange Nuts
ANSI B18.2.4.4M-1982 (R1999) — All dimensions in millimeters
| Nominal Size & Thread Pitch | Width Across Flats, S | Width Across Corners, E | Flange Dia., Dc | Bearing Circle Dia., Dw (Min) | Flange Edge Thickness, C | Thickness, M | Flange Top Fillet Radius, R (Max) |
|---|---|---|---|---|---|---|---|
| Max | Min | Max | Min | Max | Min | ||
| M5 × 0.8 | 8.00 | 7.78 | 9.24 | 8.79 | 11.8 | 9.8 | — |
| M6 × 1 | 10.00 | 9.78 | 11.55 | 11.05 | 14.2 | 12.2 | — |
| M8 × 1.25 | 13.00 | 12.73 | 15.01 | 14.38 | 17.9 | 15.8 | — |
| M10 × 1.5 | 15.00 | 14.73 | 17.32 | 16.64 | 21.8 | 19.6 | — |
| M12 × 1.75 | 18.00 | 17.73 | 20.78 | 20.03 | 26.0 | 23.8 | — |
| M14 × 2 | 21.00 | 20.67 | 24.25 | 23.35 | 29.9 | 27.6 | — |
| M16 × 2 | 24.00 | 23.67 | 27.71 | 26.75 | 34.5 | 31.9 | — |
| M20 × 2.5 | 30.00 | 29.16 | 34.64 | 32.95 | 42.8 | 39.9 | — |
Why Flange Nuts Matter
The flange diameter is substantially larger than the width across flats — an M16 flange nut has a flange diameter of 34.5 mm maximum compared to 24.00 mm width across flats. This 43.75% increase in bearing diameter translates to dramatically more bearing surface area, which:
- Reduces compressive stress on soft joint materials (aluminum, composites, plastics)
- Eliminates washer loss during field assembly and maintenance
- Prevents joint surface damage from concentrated edge loading
- Simplifies assembly by reducing the number of components per joint from three (bolt + nut + washer) to two (bolt + flange nut)
Prevailing-Torque Type Metric Nuts
This is the category that would have saved the practitioner's gearbox assemblies. Prevailing-torque nuts resist vibration-induced loosening by maintaining a frictional resistance to rotation even when no external clamping force is applied. They are the first line of defense against the most common cause of bolted joint failure in dynamic applications.
The Three Basic Designs
1. All-Metal, One-Piece Construction
These nuts derive their prevailing-torque characteristics from controlled distortion of the nut thread and/or body. The distortion creates interference between the internal and external thread flanks, generating friction that resists back-off. Common implementations include:
- Oval-distorted tops (the top portion of the nut is pressed into an oval shape)
- Beam-type deformation (slots cut into the top of the nut allow segments to flex inward)
- Thread-deforming (specific thread segments are displaced inward)
2. Nonmetallic Insert, Plug, or Patch
These nuts derive their prevailing-torque characteristics from the addition or fusion of a nonmetallic material in their threads. The nonmetallic element creates elastic interference with the mating bolt threads. Common implementations include:
- Nylon patches (a section of nylon applied to internal threads)
- Nylon plugs (a plug of nylon material pressed into a hole through the nut wall)
- Thread-locking adhesive patches (pre-applied adhesive that activates during assembly)
3. Top Insert, Two-Piece Construction
These nuts derive their prevailing-torque characteristics from an insert, usually a full ring of nonmetallic material, located and retained in the nut at its top surface. This is the classic "nylon-insert locknut" design where a ring of nylon is captured in an annular recess at the top of the nut. As the bolt threads into the nylon ring, the bolt cuts or displaces the nylon, creating elastic prevailing torque.
In the dimensional tables: Designs 1 and 2 are both designated as "all-metal type" (because design 2 uses metal nuts with nonmetallic additions rather than a separate nonmetallic insert component). Design 3 is designated as "top-insert type."
Complete Dimensional Table — Prevailing-Torque Metric Hex Nuts
ANSI/ASME B18.16.3M-1998 — Property Classes 5, 9, and 10 — All dimensions in millimeters
| Nominal Size & Thread Pitch | Width Across Flats, S | Width Across Corners, E | Property Classes 5 & 10 — Thickness, M | Property Class 9 — Thickness, M | Wrenching Height, M1 (Min) | Bearing Face Dia., Dw (Min) |
|---|---|---|---|---|---|---|
| Max | Min | Max | Min | All-Metal: Max / Min | Top Insert: Max / Min | |
| M3 × 0.5 | 5.50 | 5.32 | 6.35 | 6.01 | 3.10 / 2.65 | 4.50 / 3.90 |
| M3.5 × 0.6 | 6.00 | 5.82 | 6.93 | 6.58 | 3.50 / 3.00 | 5.00 / 4.30 |
| M4 × 0.7 | 7.00 | 6.78 | 8.08 | 7.66 | 4.00 / 3.50 | 6.00 / 5.30 |
| M5 × 0.8 | 8.00 | 7.78 | 9.24 | 8.79 | 5.30 / 4.80 | 6.80 / 6.00 |
| M6 × 1 | 10.00 | 9.78 | 11.55 | 11.05 | 5.90 / 5.40 | 8.00 / 7.20 |
| M8 × 1.25 | 13.00 | 12.73 | 15.01 | 14.38 | 7.10 / 6.44 | 9.50 / 8.50 |
| M10 × 1.5 ⚠️ (15mm) | 15.00 | 14.73 | 17.32 | 16.64 | 9.70 / 8.70 | 12.50 / 11.50 |
| M10 × 1.5 (16mm) | 16.00 | 15.73 | 18.48 | 17.77 | 9.00 / 8.04 | 11.90 / 10.90 |
| M12 × 1.75 | 18.00 | 17.73 | 20.78 | 20.03 | 11.60 / 10.37 | 14.90 / 13.90 |
| M14 × 2 | 21.00 | 20.67 | 24.25 | 23.35 | 13.20 / 12.10 | 17.00 / 15.80 |
| M16 × 2 | 24.00 | 23.67 | 27.71 | 26.75 | 15.20 / 14.10 | 19.10 / 17.90 |
| M20 × 2.5 | 30.00 | 29.16 | 34.64 | 32.95 | 19.00 / 16.90 | 22.80 / 21.50 |
| M24 × 3 | 36.00 | 35.00 | 41.57 | 39.55 | 23.00 / 20.20 | 27.10 / 25.60 |
| M30 × 3.5 | 46.00 | 45.00 | 53.12 | 50.85 | 26.90 / 24.30 | 32.60 / 30.60 |
| M36 × 4 | 55.00 | 53.80 | 63.51 | 60.79 | 32.50 / 29.40 | 38.90 / 36.90 |
Key Observation: Top-Insert Nuts Are Taller
Notice that top-insert type nuts are consistently taller than all-metal types of the same size and property class. This is because the nylon ring occupies space at the top of the nut, and the nut body must still provide adequate metal thread engagement (wrenching height, M1) below the insert. For example, an M16 property class 5/10 prevailing-torque nut has:
- All-metal type thickness: 14.10–15.20 mm
- Top-insert type thickness: 17.90–19.10 mm
This 25–35% height increase must be accounted for in joint stack-up calculations.
Wrenching Height — A Critical Safety Dimension
The wrenching height (M1) is the minimum height of the hexagonal wrenchable portion of the nut. It ensures that a wrench can adequately grip the nut during installation and removal without slipping. For prevailing-torque nuts, this dimension is particularly important because:
- The installation torque is higher than for standard nuts (you must overcome both thread friction and prevailing torque)
- Wrench slippage during installation of a prevailing-torque nut can damage the torque-generating feature, rendering the nut ineffective
- Property class 9 nuts have higher wrenching height requirements than class 5 and 10 nuts (because class 9 nuts handle higher torques)
Prevailing-Torque Metric Hex Flange Nuts
These combine the vibration-resistance of prevailing-torque design with the load-distribution benefits of an integral flange. They are the premium solution for dynamic applications on soft or thin joint materials.
Governing Standard: ANSI B18.16.3M-1998
Complete Dimensional Table — Prevailing-Torque Metric Hex Flange Nuts
ANSI B18.16.3M-1998 — All dimensions in millimeters
| Nominal Size & Thread Pitch | Width Across Flats, S | Width Across Corners, E | All-Metal Type Thickness, M | Top-Insert Type Thickness, M | Flange Dia., Dc | Bearing Circle Dia., Dw (Min) | Flange Edge Thickness, C | Flange Top Fillet Radius, R (Max) |
|---|---|---|---|---|---|---|---|---|
| Max | Min | Max | Min | Max | Min | Max | Min | |
| M6 × 1 | 10.00 | 9.78 | 11.55 | 11.05 | 7.30 | 5.70 | 8.80 | 8.00 |
| M8 × 1.25 | 13.00 | 12.73 | 15.01 | 14.38 | 9.40 | 7.60 | 10.70 | 9.70 |
| M10 × 1.5 | 15.00 | 14.73 | 17.32 | 16.64 | 11.40 | 9.60 | 13.50 | 12.50 |
| M12 × 1.75 | 18.00 | 17.73 | 20.78 | 20.03 | 13.80 | 11.60 | 16.10 | 15.10 |
| M14 × 2 | 21.00 | 20.67 | 24.25 | 23.35 | 15.90 | 13.30 | 18.20 | 17.00 |
| M16 × 2 | 24.00 | 23.67 | 27.71 | 26.75 | 18.30 | 15.30 | 20.30 | 19.10 |
| M20 × 2.5 | 30.00 | 29.16 | 34.64 | 32.95 | 22.40 | 18.90 | 24.80 | 23.50 |
Metric Hex Jam Nuts
Hex jam nuts are thin nuts used primarily as locking companions in double-nut locking systems. They are installed first (against the joint surface), then a full-height nut is tightened against the jam nut. The resulting nut-to-nut interference creates a locking mechanism that resists vibration-induced loosening.
Governing Standard: ANSI B18.2.4.5M-1979 (R1998)
Property Class: 04 (nonheat-treated) / 05 (heat-treated)
The intentionally low property class reflects the jam nut's role — it is not the primary load-carrying element. Its job is to create interference against the full-height nut above it, not to resist the full bolt tension independently.