Weld Nuts (Projection Weld Nuts for Sheet Metal Fabrication)
In sheet-metal assemblies, thread stripping and access constraints are rarely solved by “stronger bolts” alone. The real failure modes are familiar on production floors: spinning inserts, misalignment during blind assembly, and clamp loss caused by distorted parent metal or inconsistent stack-up. Weld nuts solve these issues by creating a permanent, aligned female thread directly on the base material—typically via resistance welding (projection welding / spot welding).
The product range in the image reflects common factory realities: square weld nuts (DIN 928) for high anti-rotation stability, hex weld nuts (DIN 929) for general-purpose applications, and flange/tab styles that increase weld area or provide positioning features. When specified correctly (material, plating strategy, and welding method), a weld nut becomes a controlled interface—reducing rework, preventing “nut drop” in enclosed sections, and improving takt time in serial assembly.
- Create permanent captive threads
- Enable blind-side fastening
- Prevent insert spin-out
- Support projection resistance welding
- Improve positional repeatability
- Reduce assembly rework cycles
Technical Specifications
Product Name
Weld Nuts / Welding Nuts / Projection Weld Nuts / Spot Weld Nuts
Standards
DIN 928 (square), DIN 929 (hex), ISO 21670 (weld nuts), JIS B 1196 (weld nuts), customer drawings/OEM prints
Material
Carbon steel, alloy steel; Stainless steel A2 (304) / A4 (316); aluminium programmes by request (process-sensitive)
Grades / Strength Basis
Weld nuts are specified primarily by thread class + material; for higher torque demand, choose higher-strength steel or stainless grades and validate torque capacity in the parent sheet
Diameter Range
Typical M3–M12 for sheet metal; larger sizes available depending on nut style and weld area
Common Types
Square Weld Nuts (DIN 928), Hex Weld Nuts (DIN 929), Round/Barrel weld nuts, Flange Weld Nuts, Tab Weld Nuts, Floating weld nuts (by design)
Thread
Metric coarse/fine; UNC/UNF; internal thread tolerance per ISO/ASME requirement
Surface Finish
Plain, zinc plated (blue/white), zinc-nickel; stainless passivated. Note: plating choice must match welding process and corrosion requirements.
1: Threaded inserts spin or pull out in thin gauge
What happens: Rivet nuts and inserts can lose grip under cyclic torque, especially in painted or lubricated holes; once they spin, field repair is costly.
Weld nut solution: A properly welded nut transfers load through the weld interface and surrounding sheet, not only through friction. Square weld nuts (DIN 928) also add anti-rotation geometry to resist torsional loads during service.
2: Assembly from one side (blind assembly)
What happens: Box sections, channels, and enclosed housings prevent wrench access or nut placement.
Weld nut solution: The nut is permanently located before assembly, enabling one-sided bolting and repeatable torque application.
3: Misalignment and cross-threading in production
What happens: Operators fight alignment when a loose nut can’t self-locate; cross-threading spikes scrap rate.
Weld nut solution: Piloted / non-piloted options and tab/flange features improve centring. For automated lines, the right pilot geometry reduces cross-thread starts and improves first-pass yield.
4: Joint reliability under vibration
What happens: In brackets and sheet-metal mountings, vibration loosening is amplified by loss of clamp load and micro-slip.
Weld nut solution: The nut doesn’t “solve loosening” by itself—what it does is stabilise the female thread location and reduce assembly variability. Pair it with validated locking strategy (locking bolt, patch, prevailing torque nut elsewhere) if vibration is severe.
Example reference table for common sizes. Final dimensions and tolerances must be confirmed against the required standard edition (DIN 928 / DIN 929 / ISO 21670) and your drawing.
A) Square Weld Nuts (DIN 928) — example
| Thread d | Pitch P | Across flats s (square) | Nut height m | Projection height h (typ.) |
|---|---|---|---|---|
| M6 | 1.0 | 10 | 6 | 1.2 |
| M8 | 1.25 | 13 | 8 | 1.5 |
| M10 | 1.5 | 15 | 10 | 1.8 |
| M12 | 1.75 | 18 | 12 | 2.0 |
B) Hex Weld Nuts (DIN 929) — example
| Thread d | Pitch P | Across flats s (hex) | Nut height m | Projection height h (typ.) |
|---|---|---|---|---|
| M6 | 1.0 | 10 | 6 | 1.2 |
| M8 | 1.25 | 13 | 8 | 1.5 |
| M10 | 1.5 | 15 | 10 | 1.8 |
| M12 | 1.75 | 18 | 12 | 2.0 |
What to verify before release
Weld land size vs. sheet thickness (avoid burn-through / weak fusion).
Pilot diameter (if used) vs. hole tolerance (avoid interference or tilt).
Thread class after welding (heat input can distort if process is not controlled).
Choose the welding method based on consistency, not habit
Projection weld nuts are typically selected because projections concentrate current and pressure, producing repeatable weld nuggets with short cycle time.
“Spot weld nuts” is often used in sourcing language, but the engineering requirement is usually resistance welding with controlled current, force, and time.
Material & finish selection must consider weldability
Heavy plating can interfere with stable resistance welding and increase spatter; many programmes specify weld nuts in a weld-friendly condition and protect the assembly via post-process coating.
For corrosion-critical assemblies, align coating strategy with the customer’s process route (pre-plated vs. post-coated).
Hole and fit control
If a pilot feature is used, define the hole tolerance to prevent rocking during welding.
For through-bolted joints after welding, keep clearance holes aligned to recognised practice (e.g., ISO 273 clearance holes) so torque converts to preload rather than “false torque” caused by binding.
Torque, preload, and thread protection
The nut is welded; the bolt still needs correct clamp load. Define lubrication condition and tightening method if clamp consistency matters.
In high-volume assembly, use torque-angle or validated torque values to reduce scatter. Avoid driving a bolt through spatter-contaminated threads—specify thread protection (caps/masking) or post-weld thread cleaning if required.
Quality checks that prevent field failures
Monitor weld nugget consistency (destructive peel/torque tests by lot).
Verify thread gauge pass after welding (Go/No-Go) to ensure distortion is under control.
Validate torsional capacity: “spinning weld nut” failures usually trace back to insufficient weld area or inconsistent weld parameters, not to thread strength.
Related Products
FAQ
What is a weld nut used for?
A weld nut provides a permanent threaded anchor on sheet metal or structural parts so bolts can be installed from one side. It is commonly used in sheet-metal fabrication where access is limited or where inserts may spin under torque.
What is a projection weld nut?
A projection weld nut is a weld nut designed with raised projections that concentrate current and force during resistance welding. This improves weld repeatability and cycle time compared with flat-face designs.
What is the difference between DIN 928 and DIN 929 weld nuts?
DIN 928 specifies square weld nuts, while DIN 929 specifies hex weld nuts. Square types offer stronger anti-rotation geometry, whereas hex types are a common general-purpose format.
Can stainless steel weld nuts be welded reliably?
Yes, stainless steel weld nuts can be resistance welded, but the process window is tighter and surface condition matters. Welding parameters and part cleanliness must be controlled to prevent inconsistent fusion and thread distortion.
Should weld nuts be pre-plated (zinc) before welding?
It depends on the assembly route—pre-plating can affect weld consistency and spatter, while post-coating often gives better corrosion coverage. The correct choice should be validated against welding stability, corrosion requirement, and downstream finishing.