With the rapid development of online information sharing, it is very convenient for corporate purchasers to buy fasteners such as hexagon socket head cap screws. Unlike in the past, when they had to wait for door-to-door sales or visit hardware markets to find suitable products and suppliers, the procurement process has become much less tedious today. However, incoming material inspection and acceptance have become increasingly important. Since many products are purchased online, the suppliers may not be long-term qualified partners, and enterprises often lack knowledge of the quality system and process control of new suppliers. Therefore, incoming products must be properly inspected before being put into storage and use. The following describes the standard inspection procedures and methods for hexagon socket head cap screws.
The picture below shows standard 304 stainless steel hexagon socket head cap screws. The first step is to verify that the material meets the purchasing requirements. If the material is incorrect, the screws cannot be used even if they look good, as they will not match the design specifications. The difference between 304 and 316 stainless steel screws cannot be distinguished by the naked eye. Regular manufacturers mark material codes on the screw heads, such as A2-70 for 304 stainless steel and A4-70 for 316 stainless steel. Suppliers should provide material test reports with delivery. If there are doubts about material performance, third-party authoritative test certificates can be requested.
After confirming the correct material, inspect the appearance. Visually check the surface finish for obvious burrs, eccentricity, deformation, cracks, or other defects, such as concentricity between the shank and the head. Measuring tools such as precision calipers are recommended for checking key dimensions. Each size of hexagon socket head cap screws has corresponding national standard requirements for head diameter, head height, socket dimensions, etc. Five key dimensions must be inspected carefully:
Head diameter: measured according to the tolerance range specified in national standards.
Head height: errors may occur due to insufficient mold precision, so careful verification is required.
Hexagon socket: must not be eccentric; the width across flats must be within tolerance. The hex key should fit properly without excessive looseness or tightness, as this directly affects assembly smoothness.
Thread accuracy: threads must be inspected with go/no-go gauges. The go gauge must fully enter, and the no-go gauge must not enter. Only threads meeting this requirement are considered acceptable.
Screw length: measured with calipers. Standard screw lengths are generally controlled to minus tolerance unless otherwise specified.
The above items apply to stainless steel hexagon socket head cap screws. For carbon steel screws, the following additional inspections are required:
Require suppliers to provide heat treatment reports verifying that hardness, tensile strength, and other mechanical properties meet standards.
Since carbon steel screws are usually surface-treated such as galvanizing, environmental test reports and salt spray test reports must be provided.
Although go/no-go inspection is not mandatory for threads after surface treatment, the threads must run smoothly without jamming or seizing.
Finally, check the integrity of packaging and count the quantity. Different enterprises have different management requirements: some require original factory packaging, while others follow specified packaging plans. For quantity, some deliveries must strictly match the contract; for common sizes, customers may allow the quantity based on factory packaging with small deviations, subject to mutual agreement.
