Combination screws are generally divided into two-combination screws and three-combination screws. Two-combination screws consist of a screw rod paired with either a spring washer or a flat washer. The washers can also be square washers or serrated lock washers. Three-combination screws refer to fasteners that combine a screw rod 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, and black nickel. Electroplating can be categorized into standard electroplating and environmentally friendly electroplating. Stainless steel material commonly used is SUS304. After production and processing, it only needs to be cleaned (passivated if required for salt spray resistance exceeding 48 hours).

Common reference standards for three-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 screws with spring washers and flat washers combination)

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

5. DIN912 (Hexagon socket head cap screws with spring washers and flat washers combination)

6. GB2672 (Phillips pan head machine screws with spring washers and flat washers combination)