To obtain a coating material composition for fastening members capable of easily forming a film which lowers the coefficient of friction without its scattering to obtain a stabilized torque-axial tension relationship in a short period of time.

A hexagon bolt set 1 is constituted of washers 4, a hexagon nut 3 having a female screw portion 12, and a high-strength hexagon head bolt 2 having a male screw portion 10. A liquid coating material composition comprising a phosphoric acid based extreme pressure additive, a natural resin, and liquid fats and oils is coated on each surface of the above components by dipping, and the excess is removed by centrifugation to form a film. A phosphoric acid based ester which reacts with the metal lying at each surface to form a film is used as the phosphoric acid based extreme pressure additive. A mixed oil of a drying oil which uniformly dissolves the phosphoric acid based extreme pressure additive and the natural resin to mix them and a non-drying oil is used as the liquid fats and oils. The formation of the film from the phosphoric acid based extreme pressure additive by the heat and pressure on engagement and the non-drying oil remaining in the film impart a low coefficient of friction without its scattering. Thus, a stabilized torque-axial tension relationship can be established to effect stable fastening.