Help with C# mult threaded sql binding

My goal with this program is create a class that accepts three arguments (sql statement, datagridview, db connection) and then executes the SQL command on another thread. I am having an issue when it comes to invoking the data grid. Shown below is my code.

namespace multThreadDB
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        NpgsqlConnection conn = new NpgsqlConnection();
       
        private void button1_Click(object sender, EventArgs e)
        {
            db1 d = new db1("select * from meter;", dataGridView1, conn);
            new Thread(new ThreadStart(d.fillGrid)).Start();
        }
    }

    public class db1
    {
        string sql;
        DataGridView grid;
        NpgsqlConnection conn;
        DataSet ds = new DataSet();
       

        public db1(string sql, DataGridView grid, NpgsqlConnection conn)
        {
            this.grid = grid;
            this.sql = sql;
            this.conn = conn;
        }

        public void fillGrid()
        {
            conn.Open();
            NpgsqlDataAdapter adapter = new NpgsqlDataAdapter(sql, conn);
            adapter.Fill(ds);
            SetResult(ds);
            conn.Close();
        }

        delegate void SetDataSetDelegate(DataSet parameter);

        void SetResult(DataSet ds)
        {
            try
            {
                if (!InvokeRequired)
                    grid.DataSource = ds.Tables[0];
                else
                    Invoke(new SetDataSetDelegate(SetResult), new object[] { ds });
            }
            catch { }
        }
    }
}

I receiving errors on the invoke lines. It seems the error is caused because i am invoking a control from another class? How can I fix this?

Thanks in advance!