1. Rectangular tube are marked with the nominal size and the actual size. The nominal size is an ideal size, and the actual size is the real size of the rectangular tube. Both of them are marked on the tube for the convenience of consumers to compare. 2. Deviation and tolerance of rectangular tube. Tolerance is the allowable deviation size of the square tube itself, and the deviation is a difference between the actual size and the standard size. It is pretty hard to reach the standard size, so some deviations are allowed. 3. The delivery length of the rectangular tube can be divided into ordinary length, fixed-length length and double-length length. As long as the length is within the range of contract, it called the ordinary length, the prescribed length is called the fixed-length length, and the multiples of the rectangular tube single-length length are called the double-length length. 4. The ovality of the rectangular tube. Rectangular tube may has unequal outer diameters. The difference between its large and small outer diameter is the ellipticity of the rectangular tube. The smaller the ellipticity of the rectangular tube the better. Changsha Xiangjia Metal Materical Co., Ltd. the Steel Pipe Division of ADTO GROUP, is one of the leading manufacturers of steel products in China. We specializes in manufacturing all kinds of steel pipe in various grades and sizes. Years of production experience and manufacturing facilities who have a capacity of 200,000 tons per annual will ensure the good quality and competitive duration of our products.