What is the difference between national standard and non-standard screws

National standard refers to the national standard pitch size, non-standard is based on the need or user requirements of the pitch size, in addition to the British system, American system can also be called non-national standard.

Screws, some people call it "screws" [Screw] (screws), "screw" (screw rod). In fact, the screw is commonly known as screws, screws, screws are different from each other. Screws are generally called wood screws; is the front end of the kind of pointed, larger pitch, generally used to fasten wooden parts, plastic parts. Screws are machine screws (machine screws), is the front end of the kind of flat head, pitch is smaller, uniform, generally used for fastening metal, machine parts.