Pipe, spool forming die, and pipe manufacturing method

A pipe extending from a first side toward a second side, the pipe comprising:

• a side wall separating an inside and an outside of the pipe;
• and
• a spool that is a part of the side wall formed bent so as to protrude from an outer circumferential surface of the pipe and extending to surround the outer circumferential surface,
• the spool comprising:
• a first portion located on the first side;
• and
• a second portion located on the second side,
• wherein there is a clearance between the first portion and the second portion in a top region that comprises an outer circumferential end of the spool,
• wherein the first portion and the second portion substantially abut each other in a base region located between the top region and a region of the side wall around the spool,
• wherein the spool is formed at a distance from an opening of the pipe on the second side,
• wherein the first portion in the top region comprises a straight part that extends planarly, wherein the straight part is formed in the top region and the base region,
• wherein the second portion in the top region is bent to expand toward the second side relative to the second portion in the base region,
• wherein the pipe comprises a first section, a second section, and a boundary portion, the second section including the opening on the second side, and the boundary portion being situated between the first section and the second section,
• wherein the first section and the second section are different in diameter of a cross section perpendicular to a longitudinal direction of the pipe,
• wherein the spool is disposed in the second section at a distance from the boundary portion, and
• wherein, in the second section, a diameter of the cross section of a portion of the pipe adjacent to the spool on the first side is substantially identical to a diameter of the cross section of a portion of the pipe adjacent to the spool on the second side.