Seat track mechanism for vehicle

A seat track mechanism capable of mounting to a vehicle, comprising:

• a lower rail mountable to a vehicle floor;
• an upper rail supported by said lower rail to be slidable relative to said lower rail;
• wherein said upper rail includes at least two horizontal flat portions substantially parallel to a widthwise direction of said seat track mechanism and substantially parallel to a direction of said sliding movement of said upper rail;
• and
• wherein said upper rail comprises:
• a central portion having an inverted U-shaped cross section;
• and
• two anti-detaching portions which are formed on opposite sides of said central portion in a widthwise direction thereof to prevent said upper rail from being detached from said lower rail,
• wherein said two anti-detaching portions apply a component force on said central portion so as to urge said central portion to increase a width thereof by abutting against two flanges formed on said lower rail, respectively, when a pulling load in a direction obliquely upward and lateral is imposed on said upper rail.