2. Electroplating Thickness of Threaded Fasteners
Whether barrel or rack plating is used during the electroplating process for threaded fasteners, the plating thickness obtained on each fastener in a batch varies. Even the plating distribution on the same fastener is uneven. For example, the plating thickness at the thread crest is thicker than the pitch diameter and root of the thread. The plating thickness at the ends of screws and bolts is thicker than in the middle, and this becomes more pronounced as the length-to-diameter ratio increases. The same is true for nuts. Due to the shielding effect during the electroplating process, the plating thickness on the internal threads is very thin. Only the first thread at each end is thicker than the middle portion, equivalent to the thickness on the hexagonal wrench face.
2. How to Describe the Plating Thickness of a Batch of Threaded Fasteners
In view of the uneven distribution of plating thickness on threaded fasteners, the standard cites four definitions of plating thickness: "nominal plating thickness," "batch average thickness," "local thickness," and "effective plating thickness." "Nominal plating thickness" refers to the nominal plating thickness of a threaded fastener and does not represent the actual plating thickness. The actual coating thickness of threaded fasteners is described by "effective coating thickness". "Effective coating thickness" includes "batch average thickness" and "local thickness".