The process of manufacturing combined nuts involves first forging the external hex bolts, then manually or automatically inserting flat washers onto them. After that, the threads are rolled. For larger quantities, an automatic washer inserter is used, while for smaller quantities, workers typically insert the flat washers. Naturally, the flat washers used in combined nuts are generally specialized for making combined screws. Other common flat washers are not suitable for making combined screws. Therefore, many are custom flat washers. The choice of flat washers is crucial; selecting good quality ones, like those made of Mn65 material, is ideal. Poor-quality flat washers can easily break or deform on combined screws, making them unable to spring back.