A low gloss thermoplastic composition comprises poly, a rubber-modified poly resin and an acrylonitrile containing polymer gel. At least one radially extending locking wing of the locking screw is located in at least one radial recess of the cutting head or at least one radially extending passage is formed between the locking screw and the cutting head. The connection and release mechanisms between the car seat and the base are durable and easy to operate.