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Top Fastener Manufacturer

Established in 1991


Do you know what inspection procedures a screw needs to go through before leaving the factory?

Do you know what inspection procedures a screw needs to go through before leaving the factory?

What inspection procedures do screws need to go through before leaving the factory? In fact, the screw is not only tested before shipment, but also needs to be tested all the time during the production process. When deviations in specifications or dimensions are found, production data must be adjusted immediately to reduce wasted screws.

Before a screw leaves the factory, it generally needs to undergo packaging inspection, appearance inspection, dimensional inspection, performance inspection, and actual assembly inspection.

Packaging Inspection

  1. The outer box is not allowed to be damaged, deformed or damp.
  2. The label of the outer box should have the supplier’s name, production date, OK label, inspector, specification model, material code, product color, quantity, etc. The name of incoming material should be consistent with the name of system material.
  3. Specified protective packaging materials should be used.

Visual inspection

There are two types of screw surface inspections for fasteners. One is the inspection of screws after production before electroplating, including inspection of dimensions, tolerances, etc., to see if they meet the standards or customer requirements, and the other is the inspection of screws after electroplating. That is to say, after the screw is hardened and the surface of the screw is treated, it is mainly to check the color of the coating and whether there are bad screws.

  1. Check whether the color and material of the screws meet the requirements.
  2. There shall be no abnormal phenomena such as burrs, burrs, deformation, damage, and poor processing on the surface of the screw.
  3. The coating on the surface of the screw should be uniform, and there should be no abnormal phenomena such as oxidation, rust spots, poor coating, and peeling paint.
  4. Check whether there are other abnormal phenomena such as mixed screws, short clothes, and missing accessories.

Dimensional inspection

After the screw is produced, the inspector will inspect the size of the screw to see if it meets the project requirements, including diameter, length, head cover, etc. The inspection tool is generally a vernier caliper.

performance test

The performance tests of screws include tension, torsion, hardness, penetration, corrosion resistance, etc. The smoke test can check its corrosion resistance. Put the screws in the fume box for 24 hours, then take them out for cleaning. Whether rust occurs within 24 hours of drying.

The tensile strength of the screw determines its application field, so how to test whether it meets the tensile requirements? We can test it with a pull test.

Inspection of screw coating thickness

In order to improve some performance of the screw, we usually choose to coat the surface, which can prolong the service life and play a certain protective role.

  1. Measuring method: The usage includes micrometer, vernier caliper, plug gauge, etc.
  2. Magnetic method: The magnetic method is used to measure the thickness of the coating, which is a non-destructive measurement of the non-magnetic coating on the magnetic substrate with a magnetic thickness gauge.
  3. Microscopy: Microscopy, also known as metallographic method, is to place the etched fasteners on a metallographic microscope with a micrometer eyepiece to magnify and measure the thickness of the coating on the cross-section.
  4. Chronoflow method

The liquid flow method is to pour a solution that can dissolve the coating on the local surface of the coating, and calculate the thickness of the coating according to the time required for the local coating to dissolve. There are also plating drop method, anode dissolution Coulomb method, etc.

Inspection of the adhesion strength of screw coating

There are a number of ways to assess the adhesion of a coating to the base metal, typically including the following.

  1. Friction polishing test;
  2. File method test;
  3. Scratch method;
  4. Tensile test;
  5. Thermal shock test;
  6. Extrusion method.


Screw inspection directly affects performance. Quality inspection is the oldest, and of course, the most basic means. With the continuous development of inspection technology, quality inspection must be given a wider and updated content.