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304 Stainless Steel External Hexagonal Assembly Component

The 304 stainless steel external hexagonal assembly is a fastener that preassembles the external hexagonal bolt and the matching washer (flat washer, spring washer or a combination of both) into one body. Its typical structure is: one or more non-detachable or movable washers are set under the head of the external hexagonal bolt.

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Product Description

Product introduction

The 304 stainless steel external hexagonal assembly is a fastener that preassembles the external hexagonal bolt and the matching washer (flat washer, spring washer or a combination of both) into one body. Its typical structure is: one or more non-detachable or movable washers are set under the head of the external hexagonal bolt. Users can directly install and use it without separate washers, which greatly improves assembly efficiency. In the classification of fasteners, external hexagonal assemblies are standard parts (such as GB/T 9074.17), but when their washer type, combination method or bolt size need to be adjusted to adapt to special installation conditions, they are converted into stainless steel non-standard fasteners. For example, when higher anti-loosening performance or better sealing performance is required, the standard spring washer can be changed to a serrated washer or O-ring combination. Such variant products are stainless steel special-shaped fasteners that have multiple functions such as tightening, anti-loosening, and sealing.

Product design and features

Design points:

Bolt head: Standard external hexagon, conforming to DIN 933/931 or ANSI B18.2.1 standards, easy to operate with an open-end wrench or socket.

Washer combination:

Flat washer (Type A): Increases the pressure-bearing area and protects the surface of the connected parts.

Spring washer (Type B): Provides elastic preload to prevent loosening.

Flat pad + spring pad combination: taking into account both pressure bearing and anti-loosening.

Combination method:

Non-detachable type: The washer is stuck under the bolt head and is not easy to separate, making it easy for automated assembly.

Removable: The washer rotates freely but will not come off the bolt.

Thread form: full thread or partial thread, mainly coarse thread, fine thread can also be customized.

Product features:

High installation efficiency: no need to pick and place gaskets separately, reducing assembly steps, suitable for assembly line operations.

Anti-falling design: Washers and bolts are pre-assembled into one body to avoid losing parts.

Strong corrosion resistance: 304 stainless steel is suitable for outdoor, humid and weak acid-base environments.

Flexible combination: Washers of different thicknesses and materials can be selected according to needs.

Torque stability: The assembly can avoid missing or misinstalled gaskets and ensure the consistency of tightening torque-clamping force.

Materials and application fields

Material:

Bolt material: 304 (A2), 304L, 316L optional.

Gasket material: usually the same material as the bolt, but different materials can also be selected (such as PTFE gaskets for sealing).

Mechanical properties: Bolt strength grade A2-70 (tensile strength ≥700 MPa), the hardness of the washer needs to match the bolt.

Optional treatments: polishing, passivation, pickling or electrochemical polishing.

Application areas:

Electronic and electrical: installation and fixation of power distribution cabinets, control boxes, and frequency converters.

Mechanical equipment: motor base, pump body connection, conveyor structure.

Automobile manufacturing: body accessories, light brackets, interior parts fixing (used as fasteners for auto parts).

Architectural decoration: Curtain wall keel connection, stainless steel railing fixation.

Furniture manufacturing: outdoor tables and chairs, display racks, shelf connections.

Quality control and certification system

Quality control

Raw material testing

Spectral analysis: Confirm that the Cr (18-20%) and Ni (8-10.5%) contents comply with the 304 standard.

Mechanical properties: tensile strength, yield strength, elongation test.

Dimensional inspection

Bolts: hexagonal flat, head thickness, thread accuracy (pass and stop gauge), overall length.

Washer: inner and outer diameter, thickness, flatness.

Assembly: washer moving clearance, axial movement.

Use an imager or three-dimensional coordinate measuring machine to detect key dimensions.

Mechanical performance testing

Wedge load test: Verify the bonding strength between the bolt head and the rod.

Torque-clamping force test: Determine the relationship between recommended tightening torque and clamping force.

Hardness test: Bolt HRB 67-95, washers must meet corresponding standards.

Anti-loosening performance test: vibration test (according to GB/T 10431 or DIN 65151).

Corrosion resistance test

Neutral salt spray test (NSS): No red rust for 48-72 hours.

Certification system

The general ISO 9001 quality management system covers the production process.

RoHS and REACH certifications can be provided for export to the EU.

When used in the automotive industry, it must pass the IATF 16949 system audit (as automotive parts fasteners).

When supplied as custom stainless steel fasteners, full size reports and material certifications for PPAP Level 3 are available.

Customized services

Size customization: non-standard thread specifications (such as British UNC/UNF, American system), non-standard bolt length, non-standard washer thickness and outer diameter.

Gasket modification:

Serrated lock washers (replaces spring washers)

Sealing gasket with O-ring groove

Nylon or PTFE gasket (for insulation or sealing)

Combined washer (flat washer + spring washer integrated)

Combination method: non-removable type, movable type, double washer type or multi-washer type.

Anti-loosening design: The threads are pre-coated with nylon anti-loosening glue, and the bolt heads are equipped with anti-loosening teeth (evolved into stainless steel special-shaped fasteners).

Surface treatment: mirror polishing, sandblasting, electrochemical passivation, molybdenum disulfide coating.

Process selection: CNC turning + stamping gasket combination is used for small batches, and cold heading + thread rolling + automatic assembly line is used for large batches.

FAQ

Q: What are the advantages of 304 stainless steel external hexagonal assemblies compared with ordinary carbon steel assemblies?

A: 304 stainless steel can be rust-proof for a long time without coating, and has no risk of coating peeling. It is suitable for outdoor, humid and weakly corrosive environments. However, the cost is higher and the strength is slightly lower than that of grade 8.8 or grade 10.9 alloy steel components.

Q: Will the gasket in the assembly fall off?

A: The standard assembly is designed to be non-detachable or movable. The washer is caught by the step or edge structure of the bolt head and will not fall off under normal use. However, pulling or prying too hard may cause the gasket to become detached.

Q: How to choose the appropriate assembly specifications?

A: The following factors need to be considered: ① Thickness of the connected parts (determine the bolt length); ② Tightening space (wrench space needs to be reserved for the hexagonal head); ③ Anti-loosening requirements (optional spring washers or anti-loosening washers); ④ Corrosive environment (choose 304 or 316L material).

Q: Can the assembly be used in high vibration environments?

A: Yes, but the anti-loosening design needs to be enhanced. Recommendations: ① Use serrated anti-loosening washers instead of ordinary spring washers; ② Pre-coat the threaded end with nylon anti-loosening glue; ③ Choose an assembly with a flange surface (a stainless steel special-shaped fastener). At the same time, vibration test verification is carried out.

Q: How to ensure the consistency of the tightening torque of the assembly?

A: ① Use a torque wrench to tighten to the recommended torque; ② Calibrate tightening tools regularly; ③ Conduct torque-clamping force calibration tests on the assembly; ④ For large-volume assembly, it is recommended to use automatic tightening equipment.