Gas generator and assembling method thereof

A gas generator, comprising:

• a housing provided with a gas discharge port and accommodating, therein, a gas generating agent;
• an igniter assembly accommodated in the housing, the igniter assembly including an igniter main body, which includes an ignition portion and an electro-conductive pin, a metallic collar, and a resin integrating the igniter main body and the metallic collar;
• and
• a metallic cylindrical member disposed inside the housing, the metallic cylindrical member covering the igniter assembly and defining, therein, an ignition chamber;
• the metallic collar having,
• a fixing portion including an insertion portion inserted into a hole in a bottom surface of the housing, and
• the resin having,
• a guide portion being axially in connection with the fixing portion, a portion of the metallic cylindrical member corresponding to the fixing portion and the resin having a constant diameter;
• the guide portion including a second guide portion formed axially in contact with the fixing portion, and a first guide portion formed axially in contact with the second guide portion;
• the metallic cylindrical member, the resin, and the metallic collar satisfying
• D1=D6, where D1 is an outer diameter of the fixing portion and D6 is an outer diameter of the first guide portion,
• D1>D7, where D7 is an outer diameter of the second guide portion,
• D1=D6≥R1, where R1 is an inner diameter of the metallic cylindrical member;
• and
• the metallic cylindrical member being fixed in a state in which an inner circumferential wall surface of the metallic cylindrical member and an outer circumferential wall surface of the fixing portion are press-fitted, and an annular gap is formed between the inner circumferential wall surface of the metallic cylindrical member and an outer circumferential wall surface of the second guide portion, and the inner circumferential wall surface of the metallic cylindrical member and an outer circumferential wall surface of the first guide portion are abutted against each other.