Flange Nuts
What Are Flange Nuts?
Flange nuts are hex nuts with an integrated wide bearing surface at the base that acts like a built-in washer. The flange distributes clamp load over a larger area, speeds installation, and protects the joint surface. Flange nuts are available in serrated and non-serrated styles, in inch and metric threads, and in corrosion-resistant materials and finishes.
Serrated vs. Non-Serrated Flange Nuts
- Serrated flange nuts – locking teeth bite into the mating surface to resist loosening from vibration. Best for permanent assemblies on metal where surface marring is acceptable.
- Non-serrated flange nuts – smooth bearing surface for evenly distributed clamping without surface scoring. Ideal when you want washer-like load spread and easier removal/reuse.
Materials & Finishes
- Stainless steel (18-8 / 304) – general corrosion resistance for indoor/outdoor use.
- 316 stainless steel – enhanced resistance for marine, chemical, or coastal environments.
- Zinc plated steel – economical protection for dry indoor and light outdoor exposure.
- Hot-dip galvanized steel* – heavy zinc layer for rugged exterior/structural applications.
*Availability varies by size/series. Check product grid for current options.
Common Applications for Flange Nuts
- Automotive, powersports, and machinery assemblies subject to vibration
- Sheet-metal fastening where a separate washer is undesirable
- Racking, frames, and structural brackets that benefit from wider load spread
- HVAC, electrical, and MEP support systems
- General fabrication, maintenance, and repair work
How to Select the Right Flange Nut
- Thread system & size – match inch (UNC/UNF) or metric (coarse/fine) plus diameter and pitch.
- Locking need – choose serrated for vibration resistance; non-serrated when surface finish matters.
- Environment – pick the material/finish that meets corrosion and code requirements.
- Bearing diameter – confirm flange O.D. fits the contact area and any pocket/recess.
Installation Tips for Flange Nuts
- Hand-start to avoid cross-threading; tighten with the correct wrench or socket.
- For serrated styles, seat on clean metal; avoid use with separate washers, shims, or soft coatings you don’t want marked.
- Follow project torque specs for the bolt grade/size and lubrication condition.
- Where galling is a risk (stainless-to-stainless), consider compatible anti-seize and follow spec guidance.
Standards & Fit
Flange nuts are produced to common commercial and DIN/ISO specifications with standard internal thread classes (e.g., 2B inch / 6H metric). Always verify thread, flange O.D., and height against drawings before assembly.
Flange Nut FAQs
Use the accordion below for quick answers on selection, sizing, and best practices for serrated and non-serrated flange nuts.
It combines a hex nut with a built-in washer. The flange spreads clamp load over a wider area to protect the joint and speed assembly.
Use serrated when you need vibration resistance and don’t mind tooth marks on the surface (typically bare metal). The serrations help resist loosening.
Choose non-serrated when you want washer-like load spread without surface scoring, or when you plan to remove/reuse the nut.
Generally no, flange nuts replace the separate washer. Serrated styles especially should be seated directly on the mating surface for the teeth to work.
Match thread system (inch UNC/UNF or metric), diameter, and pitch. Also confirm flange outside diameter and nut height fit your space.
Yes. Inch fine (UNF) and metric fine options are available in select sizes. Check the size list for availability.
Stainless steel is a safe default. Use 316 stainless in marine/coastal environments; hot-dip galvanized is common for rugged exterior structural work.
The teeth can mar coatings. If appearance or coating integrity is critical, choose non-serrated—or add a separate hardened washer and use a standard nut.
Follow the project spec or the fastener manufacturer’s guidance based on bolt grade, size, lubrication, and material.
Yes, the larger bearing surface helps bridge slots/oversize holes, but verify flange O.D. provides adequate coverage and meets design requirements.
Only the serrated style provides prevailing-torque resistance. Smooth (non-serrated) flange nuts are not locking; use a separate locking method if required.
They can. Use compatible anti-seize or choose dissimilar alloy pairings if your specification allows, and tighten per torque guidelines.
No. Always match the thread system, diameter, and pitch exactly to the bolt or stud.
They are often reusable, but effectiveness may decrease after multiple cycles and teeth can wear. Inspect and follow your maintenance standard.
Standards differ in dimensions like flange O.D. and height. Check your drawing/spec and select the standard that matches.