This part stipulates that the nominal diameter d1 is 1.5mm ~ 25mm, made of carbon steel or austenitic stainless steel, and the middle groove length of three mutually forming 120° longitudinal grooves on the middle surface of the pin is 1/3. Full length slot pin. The expanded diameter d2 is formed by the extruded material on each side of the groove, and d2 is greater than d1. When the grooved pin is pressed into a borehole with a diameter equal to the nominal diameter d1, a partial locking fit is formed (see Chapter 4).