A seat support for use with a vehicle seat and adapted to engage a floor-mounted track, the track having two inwardly directed lips on opposed sides of a slot. The seat support has a framework to support the seat, and which is provided with a clamping mechanism to engage the lips of the track. The clamping mechanism has two spaced apart plates, with the spaced apart plates having inwardly inclined lower regions. The lower edge of each plate carries an outwardly directed flange. A mechanism is provided to move the lower regions outwardly against an inherent resistance bias provided by the plates from an initial position in which the flanges may be inserted between the lips of the track to an outer clamping position in which the flanges engage the lips of the track. A knife element is mounted between the plates and is adapted to be moved between an upper position and a lower clamping position.