Flange Bolt Chart Selection Guide | Hebei Wotu Fastener Manufacturing Co., Ltd.
A flange bolt chart is most useful when it connects the bolt you need to the joint you are fastening: thread size, length, flange diameter, head style, property class, surface finish and the standard the drawing follows.
The first decision is to confirm what “flange bolt” means in your purchase request. It may refer to a hex flange bolt with an integrated washer face, or to bolts used on a pipe flange connection. Those are different buying problems and should not be mixed in one order.
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 MoreChart criteria
When comparing flange bolt options, check the chart against the actual mating part rather than choosing from diameter alone. The practical selection criteria are dimensional standard, thread form, under-head length, flange face style, strength class, coating and packaging or marking requirements for receiving inspection.
| Criterion | What To Check | Why It Matters | Buyer Tip |
|---|---|---|---|
| Nominal diameter and thread designation | Match the chart entry to the required thread system, diameter and pitch, then verify it against the mating nut or tapped hole. | A correct outside diameter with the wrong pitch or thread system will not assemble properly and can damage the joint. | Can you confirm the full thread callout, including diameter, pitch and thread system, for each size? |
| Bolt length and threaded length | Confirm how length is measured and compare the required grip length with the threaded portion shown in the drawing or chart. | Length that is too short may not provide enough thread engagement; excess length can interfere with surrounding parts or installation. | Please confirm the required grip length and whether the listed length is measured from beneath the head. |
| Flange diameter and bearing surface | Compare the flange diameter and underside profile with the joint clearance, hole size and the washer or load-spreading requirement. | The integrated flange spreads load without a separate washer, but an oversized flange may clash with adjacent parts or fail to seat correctly. | What maximum flange diameter and underside style can the assembly accept? |
| Head dimensions and tool access | Verify the head height, across-flats dimension and available clearance for the intended socket or wrench. | A bolt can fit the hole yet remain difficult to install if the head is too large, too tall or inaccessible. | Can you provide the head dimensions and confirm the installation tool and clearance limits? |
| Material, strength grade and surface finish | Match the specified material, mechanical grade and finish to the joint environment and the mating fasteners; request documentation if required. | These choices affect load suitability, corrosion exposure and compatibility at the joint, so a dimensional match alone is not enough. | Which material, grade and finish should be stated beside each chart size on the quotation? |
For hex flange bolts, the chart should help you check the thread diameter, thread pitch, under-head length, flange outside diameter, head width, head height and whether the underside is serrated or smooth. A serrated flange can resist loosening in some assemblies, but it may mark coated or softer mating surfaces; a smooth flange is often preferred where surface damage or controlled clamping is a concern.
For pipe flange bolting, the key chart is usually tied to the flange standard and pressure class, not only the bolt itself. The buyer must confirm the flange standard, nominal pipe size, pressure rating, number of holes, bolt circle and required bolt or stud length. A bolt that matches the thread size can still be wrong if the flange thickness, gasket and nut engagement are not considered.
Start with the governing standard. A drawing that calls for DIN, ISO, ASME or another standard changes the dimensions a supplier must hold. Do not replace a specified standard with a “similar” flange bolt unless the mating parts, wrench access and strength requirements have been checked.
Separate size from strength. Diameter and length describe fit; property class, material and heat treatment describe load capacity. A common mistake is to copy the size from an old bolt without confirming the grade marking or service condition. If the bolt clamps a structural bracket, machine guard, pipe support or equipment frame, the strength class matters as much as the dimensions.
Choose the underside and finish for the assembly. Serrated flange bolts can grip against rotation, but they can damage paint, zinc layers or softer metals. Coatings such as zinc plating or hot-dip galvanizing affect corrosion resistance and may affect thread fit, nut pairing and appearance. Ask for the finish by name rather than only asking for a “silver” or “anti-rust” bolt.
Send the details that remove ambiguity. For an inquiry, provide the standard or drawing, thread diameter and pitch, length measured from under the head, flange style, property class, finish, nut or washer requirement if any, and the working environment. If the request concerns pipe flange bolting, include the flange standard, size, pressure class, gasket type and whether you need bolts, studs, nuts or a complete bolting set.
| Criteria | Importance | Description | Example Options |
|---|---|---|---|
| Hex flange bolt vs pipe flange bolting | Critical for avoiding the wrong product category | A hex flange bolt is defined by its head and integrated flange face. Pipe flange bolting is selected around the flange connection, including hole pattern, gasket stack and nut engagement. | An equipment bracket may need a hex flange bolt, while a pipeline connection may need studs or bolts matched to the flange standard. |
| Serrated flange vs smooth flange | Important for surface protection and loosening resistance | Serrations can add grip under the head, but they may damage coatings or soft mating materials. Smooth flanges spread load without the same cutting action. | A painted bracket may favor a smooth flange, while a bare steel assembly may allow a serrated underside if the design accepts it. |
| Dimensional standard | High when parts must interchange with drawings or existing stock | Different standards can change head dimensions, flange diameter, thread length and tolerances even when the nominal thread size looks similar. | A drawing that specifies a DIN or ISO part should be quoted against that standard rather than a visually similar bolt. |
| Strength class and material | High for loaded joints and safety-related assemblies | Size controls fit, while material and property class affect the bolt’s ability to carry clamp load. Copying only the diameter and length from an old bolt can lead to an unsuitable replacement. | Two M12 flange bolts can have different property classes and should not be treated as equivalent without checking the application. |
| Surface finish and thread fit | Important for corrosion exposure, appearance and mating parts | Zinc plating, hot-dip galvanizing and other finishes affect corrosion behavior and may influence thread compatibility, nut pairing and final appearance. | Outdoor equipment may need a corrosion-resistant finish, while an indoor machine assembly may prioritize clean appearance and consistent assembly. |
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A hex flange bolt is a fastener with a built-in washer face under the head, often used in machinery, brackets, frames and equipment assemblies. Pipe flange bolting refers to the bolts, studs and nuts used to join two pipe flanges, where the flange standard, pressure class, gasket and hole pattern drive the selection.
No. Serrations can help resist rotation in some assemblies, but they can also bite into paint, zinc coating, aluminum or other softer surfaces. A smooth flange is often a better choice where surface finish, coating protection or controlled clamp load matters.
For a hex flange bolt, confirm thread diameter, pitch, length measured from under the head, head size, flange diameter and flange face type. Also state the standard, property class, material or finish requirement, and any mating nut or washer condition shown on the drawing.
Sometimes, but it should not be treated as an automatic substitution. The flange diameter, bearing area, wrench clearance, head height and underside style may change how the joint clamps and how the surface behaves during tightening.
Thread size only describes part of the fit. Length, thread pitch, strength class, coating thickness, head style, flange face and the standard behind the dimensions can all affect assembly, tightening and service performance.
Ask whether the required standard, size range, property class, finish and flange face style can be supplied for your drawing or sample. If the order is for pipe flange bolting, also confirm whether bolts, studs, nuts or complete sets are needed and provide the flange standard and pressure class.
Send the bolt standard or drawing, thread size and pitch, under-head length, flange style, property class and finish. If the bolts are for a pipe flange, also include the flange standard, size, pressure class and gasket or nut requirements.
