NRP  is  an  industry  standard,  which  stands  for,  “Non-Removable  Pin”.  On  the  center  knuckle  of  the  hinge,  there  is  installed  a  setscrew  which  tightens  against  the  groove.  This  modification  is  intended  as  a  deterrent  only.  It  is  not  to  be  considered  suitable  for  high-security  applications  or  abusive  environments.