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To set the tab-stops positions in a list box item text, you should send LB_SETTABSTOPS message. To respond to the LB_SETTABSTOPS message, the list box must have been created with the LBS_USETABSTOPS style.

const
  TabCount=4;
var
  TabStops: array[1..TabCount] of Integer=(10,15,20,30);
...
procedure TForm1.FormCreate(Sender: TObject);
begin
  TabListBox1.Perform(LB_SETTABSTOPS,TabCount,LongInt(@TabStops));
end;