Abstract: A quick-on cap (10) is provided for engaging a filler neck (22). The cap (10) includes a closure for closing the mouth of the filler neck (22) and a gripping mechanism for gripping the filler neck (22) to establish a fuel vapor seal between the closure and the filler neck (22). The closure includes a core (18) and a sleeve (14) that is movable relative to the core (18). The sleeve (14) carries a sealing ring (34) that is configured to seal against the filler neck (22). The gripping mechanism is coupled to the core (18) and sleeve (14) and grips the filler neck (22) to compress the sealing ring (34) between the sleeve (14) and the filler neck (22) in response to movement of the core (18) relative to the sleeve (14) in a cap-installation direction. The closure also includes a handle cover (12) coupled to the core (18) to make it easy for a user to move the core (18) relative to the sleeve (14) in the cap-installation direction an amount sufficient to actuate the gripping mechanism.