|Note_en=Advertising for the [[Parker 51]] model and the [[Aero-metric Ink System|Aero-metric]], citing also the ''[[Lustraloy]]'' cap. Mention also the [[Parker 21]] and some ''[[Duo-fold]]'' economic models. | |Note_en=Advertising for the [[Parker 51]] model and the [[Aero-metric Ink System|Aero-metric]], citing also the ''[[Lustraloy]]'' cap. Mention also the [[Parker 21]] and some ''[[Duo-fold]]'' economic models. |