What is the proper balance staff for 16's sangamo special 21 jewel watch?

Good question, with 7 types, 19 - 23 Jewel Open Faced and Hunter Cased SS models a Serial Number might help. That said most of them should be the same Double Roller type 16s Staff. Very hard to get. The last ones I got were from;

A Cohen Co., Boston Area, Ph: 617 523 7440

I have these available, but do not know if they are the correct staffs .
ILLINOIS BALANCE STAFF 16s #47608 D.R. S.C. NEW OLD STOCK #1684/47608

47608 should be correct, that is what I have found works.

Thanks David I have plenty if u should need any in the future.