Schema of the [[Parker]] ''"[[Jack Knife]]"'' cap seal. Excerpt from original patent ({{Cite patent|US|1028382}}) first page. Retouched by the author for a better sharpness. | Schema of the [[Parker]] ''"[[Jack Knife]]"'' cap seal. Excerpt from original patent ({{Cite patent|US|1028382}}) first page. Retouched by the author for a better sharpness. |