The core of all fasteners (excluding pins, retainer rings, etc.) lies in threads-without threads, they cannot achieve mating (except for special fasteners like rivets). Threads are regular spiral concave-convex structures machined on metal surfaces; two threads form a complete locking function through mutual rotation and mating. Among commonly used threads in China, inch threads differ from metric (national standard) threads: inch external thread accuracy grades are denoted as 1A/2A/3A, and internal threads as 1B/2B/3B; metric threads are specified by "M + diameter" (e.g., M16), with accuracy grades indicated by combinations of numbers and letters (e.g., external thread 6g, internal thread 6H). Whether metric or inch, the higher the thread grade, the higher the mating precision.

Grade 12.9 high-strength bolts are prone to corrosion during packaging, storage, or transportation. The bolts themselves meet standard requirements, but after long-distance transportation to customers, rust spots may appear on their surfaces due to various environmental factors, leading to unnecessary losses such as returns. The main cause of bolt rust is that moisture, carbon dioxide, and other components in the atmosphere corrode the material surface when in contact, eventually forming rust spots. Therefore, effective protective measures must be taken during this process.

Electroplating processes have thus emerged. Electroplating is not only to improve the appearance of bolts but, more importantly, to prevent rust. Currently, electroplating technology is quite mature, with common methods including electrogalvanizing, hot-dip galvanizing, and nickel plating. The appropriate electroplating method can be selected based on application scenario requirements.

Grade 12.9 high-strength bolts in regular use are usually not electroplated during daily use and storage. This is because electroplating on Grade 12.9 high-strength bolts can easily cause hydrogen embrittlement-a mostly uncontrollable and sudden issue that may lead to bolt breakage during use, posing serious safety hazards. All Grade 12.9 high-strength bolts undergo an oxidation blackening treatment after production. This treatment is not ordinary; unlike common blackening by boiling, it is an oxidation blackening process completed through high-temperature and strict process flows. The treated bolts have a bright black surface with a slight oily luster, which does not affect normal use, and they will not rust even after years of storage in conventional indoor environments. Some specifications of Grade 12.9 high-strength bolts in our warehouse have been stored for over a decade and show no signs of corrosion to this day.