Rega P9 + Expressimo HW

Do I need to purchase the Expressimo end stub to use with the Heavyweight or can the Expressimo heavy wt be used on the OEM stub on the RB1000 tone arm?
For the RB1000 (just like for the RB300) you shouldn't need the end-stub for the Heavyweight. The end-stub is only necessary for the RB250 which uses a threaded stock counterweight.