When manufacturing and selling screws, there will be a screw specification and screw model. With screw specifications and screw models, we can understand what specifications and sizes of screws customers need. Many screw specifications and screw models are based on the national standard specifications and models. Generally, such screws are called ordinary screws, which are generally available in the market. Some non-standard screws are not based on the national standards, specifications, models and dimensions, but are customized according to the standards required by the product materials. Generally, there is no stock on the market. In this way, we have to customize according to drawings and samples.