Parker Aerometric Full Sized Lustroloy (stainless steel) cap with chrome plated clip.  These caps had a matte finish with a brushed thin lip.  Finish was more "brushed" than the earlier caps.  The finish did not stand up to wear too well and quickly wore off.   Common Cap

Parker Aerometric Full Sized Lustroloy (stainless steel) cap with chrome plated clip.  These caps had a matte finish with no lip.  Finish was more "brushed" than the earlier caps.  The finish did not stand up to wear too well and quickly wore off.   Common Cap

Gold Filled cap and gold filled clip.  These very late production caps had "51" added to the cap lip.  Available in fountain pen, pencil and ballpoint pen.     Common Cap