![[Fastener Electroplating] Standard Introduction](https://yizhantongimage.oss-accelerate.aliyuncs.com/AutopartsMade/tieyuan/Upload/20251016165018501851.jpg!w300_1x1)
This standard specifies the dimensional requirements and coating thickness for electroplated steel and steel alloy fasteners, and provides recommendations for eliminating hydrogen embrittlement for high-tensile strength, hardened, or case-hardened fasteners. This standard applies to electroplated coatings on threaded fasteners and other fasteners. It is also generally applicable to fasteners with matching internal threads that can be cut or rolled, such as self-tapping screws, wood screws, self-drilling screws, and self-extruding screws. The provisions of this standard also apply to non-threaded fasteners, such as washers and pins.
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.
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.
A threaded insert (wire thread insert) is a new type of threaded fastener. It features a spring-shaped, concentric internal and external thread, precisely machined from high-precision diamond-shaped stainless steel wire. Once produced, the threaded insert can meet international standards for high-precision internal threads, with performance superior to threads produced by tapping.
