Why is the weight of long self tapping screws of the same specification different?

Some time ago, Mr. Li bought the same long self tapping screws in two different factories to compare their quality. But after he got the screws, Mr. Li found that their weight was different. Why is this?

The specifications and materials of long self tapping screws purchased by Mr. Li are the same. The main reason for the difference in weight is that the wire specifications used by the screw factory in production are different. For example, the same M3 screws are produced in some factories with 2.25 material, while in others with 2.5 or 2.45 material.

Just from the specification of the material itself, we know that there is a difference in weight. The larger the size of the material, the heavier the screw will be. Screws made of 2.25 material have an advantage of reducing the production cost, but there is a disadvantage that the bottom diameter of self-tapping screw becomes smaller. This screw is easier to break when used, because the force it can bear becomes smaller.

So, we measure the bottom diameter of the long self tapping screws and the torque of the test screw to see if the screw is cutting corners.