The difference between pipe markings dn, de, φ, d, and d: dn refers to the nominal diameter of the pipe. Note: This is neither the outer diameter nor the inner diameter. It is the average of the outer diameter and the inner diameter, which is called the average inner diameter. For example: dn200~φ219×6 d generally refers to the inner diameter of the pipe. d concrete. The Chinese characters on the license plate are the abbreviations of provinces, autonomous regions, and municipalities directly under the Central Government. The first letter indicates the city, region, autonomous prefecture and other prefecture-level or sub-provincial administrative regions of the province, and "a" indicates the provincial capital city. "Sichuan a" means Chengdu City, Sichuan c Zigong City, Sichuan d Panzhihua City, Sichuan e Luzhou City.
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