If you find that products with seemingly the same specifications have obvious differences in actual performance and price when purchasing 304 stainless steel butterfly screws, it is usually because of invisible parameters such as surface treatment, structural details, and material grade. Combining industry practices and supplier technical information, we have sorted out the core differences of this type of screws to help you quickly lock in the one that best suits your needs.
The first is the difference in surface treatment: it is also the key to corrosion resistance and aesthetics
The default color is natural color treatment: that is, the original color of 304 stainless steel is retained, and the appearance is silvery white. The cost is low, but the salt spray resistance is weak, usually only 72~200 hours, and it is only suitable for use in dry indoor environments, such as ordinary furniture and office equipment.
Electroplating process:
Nickel plating (matte/bright/black nickel): improve corrosion resistance (salt spray test ≥500 hours), matte nickel anti-fingerprint, bright nickel has strong decorative properties, and black nickel has both concealment and wear resistance, suitable for industrial equipment or high-end electronic products.
Galvanizing (blue zinc/color zinc): moderate cost, better protection than natural color but weaker than nickel plating, suitable for a general outdoor environment.
Passivation treatment:
Dense oxide film is formed by pickling, which significantly improves chemical corrosion resistance (salt spray test ≥500 hours), recommended for high corrosion scenes such as the chemical industry and shipbuilding.
Solution treatment:
Eliminate magnetism caused by cold working (reduced to ≤1.05 Gauss), must be used in non-magnetic environments such as medical and laboratory.
Head type and slot type configuration: functionality and operating efficiency
Head type design:
The role of pan head and flange head: increase contact surface, disperse pressure, and prevent loosening, often used in mechanical fastening scenes.
The role of countersunk head and flat head: embedded surface does not protrude, used for equipment that requires a flat appearance, such as the housing of electronic products.
Slot type selection:
Slot and cross slot: general type, low cost, but easy to slip.
Hexagon socket and hexagon socket: strong anti-torsion, but require special tools, suitable for high torque scenarios, such as automotive parts.
Knurled butterfly wing: increase hand-tightening friction, frequent disassembly scenarios, equipment maintenance preferred.
Thread specification and tolerance control: precision determines adaptability
Nominal diameter: common M4~M12, some manufacturers support M24 and above super large specifications (need to be customized).
Thread type
Full thread: full-length engagement, high tensile strength, focus on load connection.
Half thread: only part of the length has thread, reducing weight. Suitable for lightweight design, commonly used in home appliances.
Tolerance grade:
Standard tolerance: outer diameter ±0.2mm, length ±0.3mm (general scenario)
High precision: outer diameter ±0.05mm (precision instruments, aerospace field)
Material grade and mechanical properties: This 304 is not that 304
Although the same standard "304", the composition and process differences will also affect the performance:
Qualified 304 composition: Cr ≥ 18%, Ni ≥ 8% (rust-proof basis).
Low nickel version (pseudo 304): insufficient Ni content, easy to fail in salt spray test, material report required.
Strength grade: A2-70 (mainstream): tensile strength ≥ 700MPa, general mechanical scenario.
Cold forging strengthened type: upgraded to A4-80 grade (≥ 800MPa) through heat treatment, used in environments with frequent vibration (such as power equipment).
Application scenario matching suggestions
On-demand selection can balance cost and performance:
Medical and laboratory: solution treatment + surface treatment passivation under the premise of non-magnetic
Shipping and chemical industry: products are required to have high corrosion resistance, usually 316 stainless steel + passivation or 304 stainless steel + nickel-plated surface treatment
Frequent hand-tightening operation: thickened butterfly wing + knurling design, the purpose is to prevent deformation and slipping
Decorative furniture and advertising nails: use bright nickel or chrome polishing
Purchasing risk avoidance
Material authenticity: An SGS report is required to verify the Cr/Ni content.;
Salt spray test: ≥500 hours report required for high corrosion environment
Small batch verification: test the torque strength and rust resistance of the sample before the first order, especially the products with added coating.
