"Non-standard" refers to non-standard, and there are no national standards or industry standards to base on.
In China, general products have their own production standards in order to be compatible with other products (this is for the convenience of use and maintenance). For example, the "screws" we commonly use must be standard parts. If you go to any store to buy screws of the same specifications, they can be used universally.
Screw
Screw is a tool that utilizes the physical and mathematical principles of the object's inclined plane circular rotation and friction to gradually tighten the device. Screw is a common term for fasteners and a daily spoken language.
Screws are indispensable industrial necessities in daily life: extremely small screws used in cameras, glasses, clocks, electronics, etc.; general screws in televisions, electrical products, musical instruments, furniture, etc.; as for engineering , buildings, and bridges use large screws and nuts; transportation equipment, airplanes, trams, cars, etc. use both large and small screws.
Screws play an important role in industry. As long as there is industry on the earth, the function of screws will always be important. Screws are a unique invention in people's production and life for thousands of years. According to the application field, it is the first invention of mankind.
Reference materials: Baidu Encyclopedia, screws