[Alegun]

А так не проще?

Код:

const
 s1 = 'ABC'; s2 = 'EF'; s3 = 'KLMNOPSZ';
procedure TForm1.Button1Click(Sender: TObject);
var
 i1, i2, i3: integer;
begin
 for i1:= 1 to Length(s1) do
  for i2:= 1 to Length(s2) do
   for i3:= 1 to Length(s3) do
    Memo1.Lines.Add(s1[i1] + s2[i2] + s3[i3]);
end;