Combination screws are generally divided into two-piece combination screws and three-piece combination screws. Two-piece combination screws consist of a screw rod combined with either a spring washer or a flat washer; the washers can also be square washers or serrated washers. Three-piece combination screws refer to a connecting component consisting of a screw rod paired with a flat washer and a spring washer.   

       Common materials for combination screws include iron and stainless steel. Iron combination screws require surface treatment after production, such as electroplating. Common electroplating finishes include white zinc, nickel, color zinc, blue zinc, black oxide, black zinc, black nickel, etc. Electroplating treatments are divided into standard electroplating and environmentally friendly electroplating. The commonly used stainless steel material is SUS304. After production and processing, it can be cleaned and passivated if there is a requirement for salt spray resistance exceeding 48 hours.    

Common reference standards for three-piece combination screws:

1. GB/9074.13 (Cross recessed hexagon head bolts with spring washers and flat washers combination) 

2. GB/9074.17 (Hexagon head bolts with spring washers and flat washers combination)  

3. GB/9074.4 (Cross pan head with spring washers and flat washers combination)

4. GB/9074.8 (Cross small pan head with spring washers and flat washers combination)

5. DIN912 (Spring washers and flat washers three-piece combination)

Material: SUS-304 (A2-70)