Flange Bolt Selection Guide | Hebei Wotu Fastener Manufacturing Co., Ltd.
A flange bolt combines a bolt head with an integrated washer-like flange, so the joint gets a wider bearing surface without adding a separate washer. Buyers usually choose it for assemblies where speed, clamp load distribution and repeatable installation matter, such as brackets, frames, machinery covers and automotive-style bolted joints.
The main decision is not only diameter and length. You need to confirm the flange style, thread length, strength grade, coating and mating surface, because these details affect seating, loosening resistance and whether the bolt damages the assembled part.
Brand: Wotu Surface: zinc plated Specifications: in stockM6/M8/M10/M12/M14/M16/M20 Chinese national standardfull range of specifications, support nonstandard thickness, tooth pitch customized Matching: can be matched with bolts of the same specification, flat washer, spring washer complete set of shipment Packaging: 25kg cartons, whole wooden pallets
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Brand: Wotu Surface: color zinc plated, blue-white zinc plated, black oxide, hot-dip galvanized, various surface treatments available Specifications: Comply with DIN934, GB/T6170, GB/T6172.1, GB/T6177.1 standards, in stock M6-M64 full range of specifications, support nonstandard customized Packaging: woven bag inside/25kg export carton, full-container wooden pallet wrapped with film, supports private-label, neutral export packaging
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Brand: Wotu Surface: natural black oxide / hot-dip galvanized / blue-white zinc plated, multiple processes available Specifications: Based on common industry drawing parameters, suitable for pipe diameter 25mm~139.7mm, screw diameter M10~M24, total length can be nonstandard customized Matching: can be matched with nut, flat washer and spring washer of the same specifications for complete shipment Packaging: Bundling and packaging + 25kg export carton, full-container wooden pallet wrapped with film, supports private-label export packaging
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Brand: Wotu Surface: Natural black oxide treatment, customized hot-dip galvanized, zinc plated as required Specifications: Follow Chinese national standard GB/T799-1988, in stock M12-M48, total length 120mm~1500mm, nonstandard customized diameter, bending length, total screw length available Matching: Nuts, flat washers and spring washers of the same specification can be supplied in complete sets. Packaging: Bundling and packaging, using wooden pallets and film-wrapped export packaging in large quantities
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Brand: Wotu Surface: overall hot-dip zinc plating treatment Specifications: Comply with DIN and GB standards, in stock M6-M48 full range of specifications, length 20mm-300mm, supports nonstandard customized. Packaging: woven bag inside / 25kg export carton, film-wrapped wooden pallet; supports neutral packaging and customer private-label customization.
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Brand: Hengzuan Surface: color zinc plated, can be customizedblue-white zinc plated Specifications: in stock 4.8/5.5 common wire diameter, rod length 16~125mm full range of specifications, supports nonstandard customized Packaging: 25kg cartons, whole wooden pallets, support neutral packaging, private-label customization
Read MoreSelection criteria
Compare flange bolts by the features that change fit and joint performance: metric or inch thread, full or partial thread, flange diameter, serrated or smooth bearing face, head height, grade, finish and packaging needs. If the application already uses a drawing or standard part number, that reference should lead the discussion.
| Criterion | What To Check | Why It Matters | Buyer Tip |
|---|---|---|---|
| Flange face style | Confirm whether the flange bolt needs a serrated or non-serrated flange under the head. | Serrations can improve resistance to loosening on some mating surfaces, but they may mark coatings or soft materials. A smooth flange spreads load without biting into the surface. | Ask: should the flange under the head be serrated, smooth, or matched to an approved drawing? |
| Thread length and shank style | Compare the required standard, diameter, overall length, and whether the bolt is fully threaded or partly threaded. | The wrong thread length can leave threads in the shear plane, prevent full clamping, or stop the nut from tightening correctly. | Send the mating part thickness, washer use if any, nut height, and required protruding thread after assembly. |
| Strength grade and mating nut compatibility | Specify the bolt grade or property class and confirm the matching nut grade required for the joint. | A strong bolt paired with the wrong nut can strip, loosen, or fail to achieve the intended clamp load. | Ask: what bolt property class and nut grade are required by the drawing, project standard, or equipment manufacturer? |
| Coating and corrosion exposure | Define the finish, such as plain, zinc plated, or hot-dip galvanized, based on the working environment and mating components. | Coating affects corrosion resistance, thread fit, torque behavior, and appearance. Thick coatings may require compatible nuts or thread allowance. | Ask whether the bolt will be used indoors, outdoors, near moisture, or with galvanized parts, and confirm the required finish on the purchase order. |
| Head and wrench clearance | Verify flange diameter, head height, across-flats size, and available tool access around the joint. | A flange head can replace a washer in some assemblies, but the larger bearing surface may interfere with nearby walls, slots, or raised features. | Provide a drawing or photo of the joint area and ask whether the proposed flange bolt head will clear the surrounding parts and tools. |
The most practical distinction is between a serrated flange bolt and a non-serrated flange bolt. A serrated flange can bite into the mating surface and help resist loosening, but it may mark painted, plated or softer materials. A smooth flange spreads load more gently and is often preferred where surface damage, corrosion protection or controlled torque is a concern.
Flange bolts are also not a direct substitute for every hex bolt and washer combination. The built-in flange changes the contact area and installed height, so buyers should check clearance around the head, the hole size, the mating material and the required tightening method before changing an existing design.
Start with the joint, not the bolt drawing alone. Confirm the material being clamped, whether the surface is flat or slotted, and whether the bolt head has enough room to seat fully. A flange bolt works best when the flange sits evenly; on uneven castings, oversized holes or soft materials, the flange may not support the load as intended.
Choose the flange face to match the assembly. Serrations can improve grip in vibration-prone joints, but they can remove coating and create a corrosion point. A non-serrated flange is cleaner for finished surfaces and assemblies that need predictable torque-tension behavior, but it may need a separate locking method if vibration is severe.
Match thread, grade and finish to the mating nut or tapped hole. Avoid mixing incompatible thread standards, unclear property classes or coatings that change fit. Zinc plating, hot-dip galvanizing, black finish and other surface treatments can behave differently in threaded engagement, so confirm the finish and matching internal thread before ordering in volume.
For an inquiry, send the diameter, thread pitch or standard, length, flange type, head style, strength grade, surface finish and quantity. If the part replaces an existing fastener, include a drawing, photo or sample details so Hebei Wotu Fastener Manufacturing Co., Ltd. can check the key dimensions rather than guessing from a short description.
| Criteria | Importance | Description | Example Options |
|---|---|---|---|
| Flange face | High impact on surface condition and loosening resistance | Serrated faces can grip the mating surface, while smooth faces spread load with less marking. The right choice depends on vibration, coating sensitivity and whether the surface can be damaged. | A painted bracket may suit a smooth flange better; a hidden steel joint with vibration may justify a serrated face. |
| Thread and length | Critical for fit and clamp engagement | Diameter, pitch, overall length and thread length must match the nut or tapped hole. Full-thread and partial-thread bolts behave differently in joints with varying grip thickness. | A replacement part should be checked against the original bolt drawing rather than described only as an M-size bolt. |
| Strength grade | Essential for load-bearing joints | The bolt grade must suit the joint load and the mating internal thread. Using a stronger bolt does not automatically improve the assembly if the nut, tapped hole or clamped material is the limiting point. | A machinery cover and a structural bracket may require different property classes even if the diameter is the same. |
| Surface finish | Important for corrosion exposure, appearance and thread compatibility | Coatings change how the bolt seats, looks and resists corrosion. Some finishes also affect thread fit or require matching nuts, especially on thicker coatings. | A hot-dip galvanized fastener may need confirmation of compatible internal threads before volume ordering. |
| Mating surface and hole condition | Often overlooked but important for reliable seating | A flange bolt works best when the flange sits flat and has enough bearing area. Uneven castings, slotted holes or soft materials may need design review or a different fastening method. | An oversized slot may need a separate washer or another joint design rather than relying only on the flange. |
Related Options
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Choose serrated when the joint needs extra resistance to rotation and the mating surface can tolerate bite marks. Choose a smooth flange when the part is painted, plated, soft, or when controlled torque and surface protection matter more than mechanical biting.
Sometimes, but it should not be treated as an automatic swap. The built-in flange changes the bearing diameter, head clearance and installed height, so check the hole size, surrounding clearance, mating surface and tightening method before changing the fastener.
Confirm diameter, thread pitch or standard, length, strength grade, flange type, head style, surface finish and quantity. If the bolt must match an existing part, provide a drawing, sample dimensions or clear photos so the head, flange and thread details can be checked.
No. The flange provides a wider bearing surface and reduces separate washer handling, but it does not perform every washer function. Special washers may still be needed for oversized holes, soft materials, sealing, electrical isolation or specific locking requirements.
The finish should match the exposure, mating thread and appearance requirement. Zinc plating, hot-dip galvanizing, black finish and other treatments can affect corrosion behavior and thread fit differently, so confirm the coating and compatible nut or tapped hole before bulk purchase.
Send the bolt diameter, thread pitch, length, flange type, grade, finish and quantity. Add a drawing, standard reference or photo if the bolt must replace an existing part.
