What are the descriptions of the types of fittings?

There are many types of stainless steel pipe fittings, and the following main types are summarized: 1. Variable diameter pipe fittings; 2. a pipe with a variable wall thickness; 3. Change the section of the pipe; 4. Curved pipe fittings...
     1. Variable diameter pipe fittings, in which the diameter of a pipe end or a part of the pipe is reduced;
     2. A pipe member with a variable wall thickness means that the wall thickness changes along the length of the pipe;
     3. Change the section of the pipe, according to requirements, the circular section into a square, ellipse, polygon, etc.;
     4. Bending pipe fittings, we have more contact, which is to bend the straight pipe into bends with different radius of curvature, such as elbows, bends, etc.;
     5. a tubular member having a flange and a rounded edge, the former means that the end of the pipe is convex toward the inner side or the outer side, and the latter means a pipe member which forms a bulge or a groove in the circumferential direction of the pipe;
     6. a pipe fitting with a crimping and sealing type, which increases the total strength of the pipe end to the outer side or the inner side of the pipe or to seal the pipe end;
     7. Expanding the pipe fittings, and expanding the ends or parts of the pipe fittings to form pipes of various shapes as required;