Violation of PRIMARY KEY constraint 'PK_Auto_Part_Details'. Cannot insert duplicate key in object 'dbo.Auto_Part_Details'. The duplicate key value is (1).

private void btn_Add_Click(object sender, EventArgs e)
{
    try
    {
        for (int i = 0; i < dgv_Add_job_card.Rows.Count ; i++)
        {
            con.Open();
            s = "insert into Auto_Part_Details (Items_No, Job_Card, Value_Part, Auto_Parts_id) values (@Items_No, @Job_Card, @Value_Part,@Auto_Parts_id )";
            sd=new SqlCommand(s,con);
            sd.Parameters.AddWithValue("@Items_No", dgv_Add_job_card.Rows[i].Cells[0].Value);
            sd.Parameters.AddWithValue("@Job_Card", dgv_Add_job_card.Rows[i].Cells[1].Value);
            sd.Parameters.AddWithValue("@Value_Part", dgv_Add_job_card.Rows[i].Cells[2].Value);
            sd.Parameters.AddWithValue("@Auto_Parts_id",dgv_Add_job_card.Rows[i].Cells[3].Value);
            sd.ExecuteNonQuery();
            con.Close();
        }
    }