The TracKnob comes in male and female version. The knobs are sold individually. The dimensions of the TracRac TracKnob are 3" high, 3" wide, and 3" in depth. A TracRac TracKnob is used on the crossbars of the TracRac Overhead Rack, TracRac Base Rail Tiedowns, and cargo holders. The TracRac TracKnob is a spare or replacement part.