Metric Class 10.9 Plain Steel Non-Serrated Flange Nuts
Class 10.9 Metric Non-Serrated Flange Nuts in Plain Steel Finish—also called smooth flange nuts, plain flange nuts, washer face nuts, or free-spinning flange nuts—combine a standard hex nut with an integrated flat washer flange at the base, delivered in an uncoated configuration for maximum application flexibility. Unlike serrated flange nuts that grip and dig into surfaces, non-serrated flange nuts feature a smooth bearing surface that allows the nut to rotate freely during tightening without scratching, marring, or damaging the material underneath. The plain steel finish makes these fasteners ideal for assemblies destined for painting, powder coating, or other post-installation surface treatments—or for high-temperature applications where zinc plating would degrade.
Why Choose Plain Finish Non-Serrated Flange Nuts?
The combination of a smooth flange and plain steel finish creates the ultimate surface-friendly, finishing-ready fastener. The non-serrated flange spins freely without marking or scarring the mating material during installation, preserving surface quality for subsequent coating processes. The uncoated steel accepts paint, powder coat, e-coat, and other finishes with excellent adhesion, unlike zinc plated fasteners that may require special primers or surface preparation. For OEM manufacturers and custom fabricators who coat entire assemblies after construction, plain finish non-serrated flange nuts deliver the ideal combination of strength, surface protection, and coating compatibility.
Why Choose Plain Finish Over Zinc Plated?
While zinc plated fasteners offer built-in corrosion resistance, plain finish fasteners are the preferred choice in several key scenarios. High-temperature applications benefit from plain steel because zinc plating can off-gas, discolor, or lose integrity at elevated temperatures, plain steel maintains consistent performance without coating degradation. Post-assembly finishing such as painting, powder coating, e-coating, or hot-dip galvanizing adheres better to clean, uncoated steel surfaces. Controlled indoor environments where corrosion is not a concern can use plain fasteners at lower cost. OEM and manufacturing applications often specify plain finish when assemblies undergo system-wide coating processes after fastener installation.
Why Choose Class 10.9 Steel?
Class 10.9 steel provides a minimum tensile strength of 1,040 MPa (150,000 PSI) and yield strength of 940 MPa, approximately 25-30% stronger than Class 8.8 fasteners and the metric equivalent of SAE Grade 8. This makes Class 10.9 non-serrated flange nuts essential for heavy-duty assemblies, high-torque applications, and critical joints where fastener failure is not an option. The combination of high strength and a smooth, surface-protecting flange makes these nuts ideal for demanding applications where both performance and finish quality matter.
Material & Specifications
Our Class 10.9 plain steel metric non-serrated hex flange nuts are manufactured from quenched and tempered alloy steel, heat-treated to achieve the mechanical properties required for high-stress fastening applications. Class 10.9 is the metric equivalent of SAE Grade 8, the highest strength grade commonly available for commercial fasteners. The plain steel finish leaves the base metal exposed and ready for custom coating processes, or suitable for use in applications where corrosion protection is provided by other means such as oil, grease, or environmental controls.
Plain Steel in High-Temperature Applications
Zinc plating begins to degrade around 400°F (200°C), making it unsuitable for engine compartments, exhaust-adjacent components, industrial ovens, and other high-heat environments. Plain steel Class 10.9 fasteners maintain their full mechanical properties at temperatures well beyond this threshold, making them the correct choice for thermal-critical applications. When surface protection is also required in these environments, non-serrated flange nuts ensure that heat-sensitive painted or coated surfaces won't be damaged during fastener installation or removal.
Serrated vs. Non-Serrated: Which Do You Need?
Choosing between serrated and non-serrated flange nuts depends on your application requirements. Serrated flange nuts feature teeth on the flange that bite into the mating surface, providing vibration resistance and locking action, but they permanently mark the surface and are incompatible with post-assembly coating where appearance matters. Non-serrated (smooth) flange nuts allow free rotation and protect surface finishes but do not provide inherent locking capability. For applications requiring vibration resistance with a smooth flange nut, consider using a thread locker compound, pairing with a separate lock washer, or selecting a prevailing torque flange nut instead.
Common Applications
Class 10.9 plain steel metric non-serrated flange nuts are specified across industries where high strength, surface protection, and finish flexibility are required:
- Automotive & Motorsports: Body panels, chassis assemblies, interior components destined for paint or powder coat
- Heavy Equipment & Machinery: Frames and enclosures scheduled for post-weld coating, high-temperature assemblies
- Agricultural Equipment: OEM implement assemblies, components for e-coat or paint lines
- Industrial & Manufacturing: Equipment housings, guards, and covers undergoing batch coating processes
- OEM & Custom Fabrication: Any assembly where fasteners must accept the same finish as surrounding components
Plain vs. Zinc Plated: Quick Comparison
Choose Plain Finish when: Operating temperatures exceed 400°F, assembly will be painted or coated after installation, appearance requires fasteners to match surrounding finishes, application is in a controlled indoor environment, or cost savings are prioritized over built-in corrosion resistance.
Choose Zinc Plated when: Corrosion resistance is needed immediately upon installation, fasteners will be exposed to moisture or outdoor conditions, or no post-assembly coating is planned.
Available Sizes
We stock Class 10.9 plain steel metric non-serrated flange nuts in a range of popular thread sizes to cover most heavy-duty and finishing-sensitive applications. Albany County Fasteners offers competitive bulk pricing and same-day shipping on in-stock items to keep your production on schedule.
Need a zinc plated version or different strength grade? Contact our team—with over 18 million fasteners in stock, we can help you source the right flange nut for your specific requirements.