Chapter 3 of the standard defines "batch average thickness." The plating thickness of threaded fasteners cannot be represented by the coating thickness of a single part. Regardless of whether threaded fasteners are processed using rack or barrel plating, not every part in the same batch will achieve the same coating thickness. However, thickness variation follows a normal distribution. We assume that the coating thickness is uniformly distributed across the surface of the batch to calculate the average coating thickness. This leads to the concept of "batch average thickness," which can be used to describe the coating thickness of an entire batch of threaded fasteners. In Table 1 of the standard, "batch average thickness" is expressed as a range. The minimum batch average thickness is the requirement for ensuring corrosion protection of threaded fasteners, while the maximum batch average thickness is required to ensure thread engagement after plating.

"Local thickness" in the standard actually refers to the minimum local thickness, which describes the minimum specified coating thickness on a specified local test surface of a threaded fastener. The test verification data shows that the local coating thickness values ​​measured on the specified local test surfaces, such as the screw and bolt heads and the wrenching surfaces of the screws, bolts, and nuts, are all greater than the batch average thickness values. Generally, the batch average thickness value meets the requirements, and the minimum local thickness also meets the requirements. The test results also confirm that the numerical relationship between "nominal coating thickness," "batch average thickness," and "local thickness" is correct, which constitutes the theoretical basis for the detection and acceptance of the electroplating thickness of threaded fasteners.