Generally, the screws we refer to are without washers, such as keyboards, telephones, plug-ins, routers and other products, which are directly locked by screws without washers. The screws of these products can be locked by screw machines, but some products use washers when locking screws. The washers are easy to fall off, so you need to place the washers yourself. If the gasket and screw should not be separated, this situation can be used, depending on the actual situation.