10/08/2026
How to avoid buying bad quality screws?
Screw is very important in our daily life, and good quality screws is very critical for machines.
The problems we are mostly facing are:
Misrepresentation of Materials and "Cutting Corners":
Stainless steel grade confusion: Passing off 201 or 304L stainless steel as 304 or 316 grades, or using materials that fail to meet salt spray test requirements for corrosion resistance.
Substandard carbon steel grades: Procuring high-strength screws (Grade 8.8 or 10.9) that lack sufficient quenching hardness or are made from low-carbon steel substitutes, leading to stripped threads or breakage during use.
Dimensional Tolerances and Thread Profile Defects:
Non-standard thread profiles (e.g., tolerance deviations, thread tips that are too blunt or too sharp), causing stripped threads, galling (seizing), or inability to screw on the nut during assembly.
Head shape tolerance issues (e.g., incorrect countersink angles, hex or Phillips recesses that are too shallow or too deep), resulting in installation tools slipping (cam-out) or uneven surface finishes.
Hydrogen Embrittlement Failure (A critical issue for high-strength screws):
For electroplated high-strength screws (Grade 10.9 and above), incomplete hydrogen relief (dehydrogenation) after pickling and plating can lead to sudden, delayed fracture (hydrogen embrittlement) after a period of use.
Inconsistent Surface Treatment Quality:
Peeling zinc plating or uneven coating thickness causing a sharp drop in corrosion resistance, or excessively thick plating causing threads to jam during assembly.
How to deal with this problemοΌ
Many quality issues stem from vague procurement specifications, leaving room for substandard suppliers to cut corners.
**Precision in Drawings and Standards:**
Clearly specify standard numbers (e.g., DIN 912, ISO 4762, GB/818); do not simply state "M6Γ20 screw."
Clearly define tolerance classes (e.g., thread tolerance 6g/6H), head shape tolerances, and recess depth requirements.
**Precision in Material and Performance Grades:**
Avoid vague terms (such as "stainless steel" or "high strength"); specify exact grades or classes (e.g., SUS304/SUS316; carbon steel grade 8.8/10.9/12.9).
For stainless steel intended for highly corrosive environments, explicitly mandate Positive Material Identification (PMI) testing requirements in the contract.
**Surface Treatment and Salt Spray Test Standards:**
Clearly specify the coating type (e.g., electro-galvanizing, hot-dip galvanizing, Dacromet, micro-zinc) and coating thickness requirements.
Quantify salt spray test duration (e.g., "Neutral Salt Spray (NSS) test: no red rust for at least 72 hours") and require that a test report be provided with the shipment.
