9/16"-18 Serrated Hex Flange Nut — Black Finish — 7/8" Hex (FPN916L)
Fine-thread serrated flange nut engineered for U-bolt clamping applications. Provides vibration resistance, consistent preload, and washer-free installation for trailer suspension systems.
Overview
The FPN916L is a 9/16"-18 UNF serrated hex flange nut designed for high-load clamping in trailer suspension assemblies. The integrated serrated flange eliminates the need for a washer while providing locking resistance against vibration, making it ideal for U-bolt applications such as spring seats, axle mounts, and tie plates.
R&P Service Insight
In real-world trailer service, flange nuts like this are critical for maintaining clamp load across leaf spring packs and axle seats.
- Serration Advantage: Bites into mating surface to resist loosening under vibration.
- No Washer Required: Built-in flange distributes load evenly across tie plates.
- Fine Thread Control: 9/16"-18 thread allows more precise torque application and stronger clamping force.
R&P Knowledge Hub
Compatibility: Designed for 9/16"-18 UNF threaded fasteners including UB-R303 U-bolts and similar suspension hardware.
Vehicle / System Fit: Common in trailer axle mounting systems, leaf spring suspensions, and heavy-duty tie plate assemblies.
Installation Notes: Serrated flange must seat directly against clean metal surface. Do not reuse heavily worn or flattened serrated nuts.
Performance Insight: Fine-thread fasteners provide higher clamp load with less torque variation, while serrations prevent loosening under cyclic load.
R&P Repair Insight
When replacing U-bolt hardware, the nut is just as critical as the bolt. Reusing old nuts can lead to clamp loss and premature suspension wear.
- Thread Match: Confirm 9/16"-18 fine thread—coarse thread nuts will not engage correctly.
- Serration Condition: Replace if serrations are worn or flattened.
- Torque Retention: Always recheck torque after initial road use on new installs.
Features
Serrated Locking Flange
Integrated serrations resist loosening and eliminate the need for a separate lock washer.
9/16"-18 Fine Thread
Provides increased clamping force and finer adjustment compared to coarse thread hardware.
7/8" Hex Drive
Standard wrench size ensures compatibility with common trailer service tools.
Black Finish
Corrosion-resistant coated finish suitable for exposed trailer suspension environments.
Specifications
| Specification | Detail |
|---|---|
| Part Number | FPN916L |
| Product Type | Serrated Hex Flange Nut |
| Thread Size | 9/16"-18 UNF (Fine Thread) |
| Hex Size | 7/8" (0.86" measured) |
| Flange Diameter | ~1.10" |
| Overall Height | ~0.48" |
| Hex Height | ~0.32" |
| Flange Thickness | ~0.12" |
| Finish | Black Coated |
Fitment / Application
| Category | Details |
|---|---|
| Vehicle / System | Trailer Suspension Systems |
| Primary Fit | UB-R303 U-Bolts (9/16"-18) |
| Secondary Fit | Leaf spring U-bolt assemblies, axle tie plates |
| Notes | Must match fine-thread U-bolts; not compatible with 9/16"-12 coarse thread |
Included Components
| Quantity | Item |
|---|---|
| 1 | 9/16"-18 Serrated Hex Flange Nut (FPN916L) |
