10-32 button-head cap screw that holds the front of the gripframe to an Automag or Minimag mainbody. This is the shorter screw for AM/MM only.
For Tac One, RT Pro, RT ULE Custom or Emag with ULE or Tac One Mainbody, purchase Part#1557.  This is a slight longer screw that works with the taller ULE  and PRO Rails.