just checked  theres  a bunch of these on ebay  for a better  price just type  in  fender roller  nut

they give you these little pieces of  metal to put  under the   roller  bridge  if you  remove too much wood. there  different  thicknesses  to bring the   nut  up to proper  height.  if you  do it  right  you dont  have  to shim it  you just  screw  it  down and your  set.

                                                    but since  its  not  an easy  thing  to get it  perfect  first  time  they  give  you  those  shims  to  make everything  right  if  you make a  mistake.   i didnt  need  them.