Combination nuts refer to a three-piece assembly consisting of a hex bolt, a spring washer, and a flat washer, all tightened together. Combination nuts are also known as hex combination bolts or hex combination nuts. There are two standards for them in China. One type is the electroplated cross-slot hex combination nut, which comes in environmentally friendly and non-environmentally friendly options, the latter being the standard. Commonly used environmentally friendly electroplating includes environmentally friendly galvanized, environmentally friendly blue zinc, environmentally friendly white zinc, and environmentally friendly nickel. Non-environmentally friendly options include colored zinc, white zinc, black zinc, and white nickel. After electroplating, the salt spray test duration for combination nuts is generally 72 hours for environmentally friendly galvanized and blue zinc, while environmentally friendly white zinc has a shorter duration of 6-8 hours. The bolt has a national standard number of GB9074.13. The other type is the cross-slotless hex combination nut, also known as the trimmed edge hex combination nut.