Fuel tank cap and fuel filler device for a vehicle

A fuel filler device adapted to be connected with a fuel filler pipe, comprising:

• an adaptor securely connected with the fuel filler pipe, said adaptor including a surrounding wall extending longitudinally, and two engaging protrusions projecting radially from an inner peripheral surface of said surrounding wall and radially spaced apart from each other, said engaging protrusions extending circumferentially and being angularly spaced apart from each other by two access slots, each of said engaging protrusions having a guiding portion which extends from one of said access slots toward another one of said access slots, and a retaining portion which projects downwardly from said guiding portion adjacent to said another one of said access slots, said guiding portion having a guiding surface which faces downwardly and which is inclined upwardly from an end adjacent to said retaining portion toward another end distal from said retaining portion;
• and
• a fuel tank cap removably and longitudinally insertable into said adaptor, said fuel tank cap including a gripped cap body which is disposed on said adaptor to cover an upper opening of said surrounding wall, an insert portion which extends downwardly from a bottom surface of said gripped cap body to be rotatably inserted into said surrounding wall, and two retained protrusions which project radially from an outer peripheral surface of said insert portion and are diametrically opposite to each other, said two retained protrusions being moved longitudinally with said insert portion to respectively pass through said access slots, each of said retained protrusions having a press-fit surface which faces upwardly, and a first retained slot and a second retained slot which are recessed from said press-fit surface and angularly spaced apart from each other, wherein said fuel tank cap is operably rotated relative to said adaptor between an opened position, where said retained protrusions are aligned with and disposed downwardly of said access slots, and a closed position, where said press-fit surface of each of said retained protrusions abuts upwardly against said guiding surface of a corresponding one of said engaging protrusions, and said retaining portion of each of said engaging protrusions is engaged downwardly in either said first retained slot or said second retained slot of a corresponding one of said retained protrusions.