Gear and electric power steering device

A gear comprising:

• a metal core comprising a disc portion that extends radially relative to a rotation axis of the gear, and an axially extending cylindrical portion having one axial end connected to a radially outer portion of the disc portion, as well as an other axial end;
• a plurality of rotation prevention grooves formed on a radially outer peripheral portion of the cylindrical portion, and a plurality of rotation prevention grooves formed on a radially inner peripheral portion of the cylindrical portion;
• a synthetic resin tooth body integrally coupled to said cylindrical portion by filling both said plurality of rotation prevention grooves formed on the radially outer peripheral portion of the cylindrical portion, and said plurality of rotation prevention grooves formed on the radially inner peripheral portion of the cylindrical portion, with material of the synthetic resin tooth body;
• and
• a guard portion that extends outwardly in a radial direction from the other axial end of the cylindrical portion, wherein
• the rotation prevention grooves formed on the outer peripheral portion extend axially from the one axial end to the guard portion and are formed by compression forming,
• the rotation prevention grooves formed on the inner peripheral portion extend axially from the other axial end to the disc portion and are formed by compression forming, and
• the metal core is formed by compression forming.