304 Stainless Steel Round Head Square Neck Screws

Product introduction

304 stainless steel carriage screws, also known as round head square neck screws or carriage bolts, are screws with a smooth hemispherical head and a square clamping structure under the neck. Its design feature is that when installed, the square neck will snap into the square hole of the connected piece, thereby preventing the screw from rotating with the nut, and no additional tools are needed to fix the head. In the classification of fasteners, carriage screws themselves are standard parts, but when their head size, square neck length or thread specifications need to be adjusted to adapt to the special installation environment, they are converted into stainless steel non-standard fasteners. For example, in wooden structures or sheet metal connections, it is sometimes necessary to shorten the height of the square neck or increase the diameter of the head. Such modified products are stainless steel special-shaped fasteners that have both beautiful appearance and anti-rotation functions.

 

Product design and features

Design points:

Head shape: hemispherical or oblate head, smooth surface, no tool groove.

Anti-rotation structure: square neck under the head (commonly the opposite side width is slightly larger than the thread diameter).

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

End treatment: plain end, chamfered end or guided tapered end.

Product features:

Excellent anti-rust performance: 304 stainless steel has good resistance to atmospheric, water, and weak acid and alkali corrosion.

Easy to install: the square neck is self-locking and anti-rotating, and the nut can be tightened by one-sided operation.

Beautiful appearance: Round head without groove design, suitable for exposed occasions.

Moderate strength: 304 material strength level is about A2-50 or A2-70.

 

Materials and application areas

Material:

Grade: 304 (A2), 304L, 316L optional.

Mechanical properties: tensile strength ≥500 MPa (A2-70 grade).

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

Application areas:

Outdoor wooden structures: wooden boardwalks, park seats, outdoor play facilities.

Architectural decoration: glass curtain wall fixtures, stainless steel railing connectors.

Transportation: carriage floors, container locks.

Ship equipment: deck accessories, outfitting parts (316L recommended)

 

Quality control and certification system

Quality control:

Dimensional inspection: The diameter of the head, the opposite edge of the square neck, and the length of the thread are inspected with a pass-and-stop gauge and an imager.

Mechanical properties: Carry out hardness test (HRC or HV), wedge load test.

Corrosion resistance test: 48~72 hours neutral salt spray test (according to GB/T 10125).

Material verification: Spectral analysis confirms that the Cr and Ni content meet the 304 standard.

Certification system:

The general ISO 9001 system covers the production process.

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

When used in bridge or curtain wall projects, third-party inspection reports can be provided according to customer requirements.

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 length (such as 250mm, 300mm), non-standard thread (such as fine thread M10×1.0), square neck size adjustment.

Head modification: enlarge the diameter of the head, and open a cross recessed or hexagonal hole in the head (at this time, it evolves into a stainless steel special shape fastener).

Anti-loosening design: pre-coated nylon anti-loosening glue, thread tail punching point or necking.

Surface treatment: polished to mirror surface, sand blasting, electrochemical passivation.

Batch process: CNC turning + square neck milling for small batches, cold heading + thread rolling process for large batches.

 

FAQ

Q: What are the advantages of 304 stainless steel carriage screws compared with galvanized carbon steel carriage screws?

A: 304 stainless steel can be rust-proof for a long time without coating, there is no risk of coating peeling, and the corrosion resistance life is much better than galvanized parts. However, the cost is higher and the strength is slightly lower than 8.8 grade carbon steel.

 

Q: Can it be used in outdoor coastal environments?

A: 304 may cause pitting corrosion in coastal environments. It is recommended to upgrade to 316L stainless steel. If you insist on using 304, you should add passivation treatment and perform regular maintenance.

 

Q: What should I do if the square neck cannot be clamped?

A: Check whether the square hole size of the connected parts matches. If the standard square hole is still loose, you can customize stainless steel non-standard fasteners to enlarge the opposite side of the square neck, or add anti-rotation glue to the square neck.

 

Q: Can this screw be used as a stainless steel non-standard part for food machinery?

A: Yes, but it must be ensured that the surface roughness Ra≤0.8μm and there is no residual material in the gap. It is recommended to use passivation treatment and comply with FDA or EU 1935/2004 food contact material requirements.

 

Q: Can the head dome be processed with patterns or logos?

A: Yes. A LOGO or identification symbol can be added to the cold heading mold. This belongs to the category of stainless steel special-shaped fasteners. It is necessary to evaluate the mold processing cost and minimum order quantity.

 

Q: What is the minimum order quantity?

A: The minimum order quantity for standard specifications is low. However, if it is 304 stainless steel non-standard parts, especially customized stainless steel fasteners that require a new mold, there is generally a minimum order quantity requirement, which depends on the dimensional complexity and the feasibility of cold heading.

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