Jeffries Banknote Company - subcontractor to American Banknote Co.. for the 1991 $14 postage stamp (Scott 2542).

Jenny - see Inverted Jenny.

Joint Issue - stamps issued by two or more countries simultaneously, with similar designs, honoring the same person or event.  Example: 1975 Apollo-Soyuz Space Issue, Scott 1569-1570.

*Joint Line - the printed line produced on the web by the rotary press at the point where two plates met.  Two plates were used in combination with each other on the classic rotary press.  Each plate would fit over half of the printing cylinder.  Ink would gather in the joints between the plates, leaving an impression (a joint line) on the web.  One complete revolution of the press cylinder created two joint lines on the web.  Joint lines were produced on both sheet and coil stamps, but only those produced on the coil stamps are commonly collected.  A Joint Line is not the same as a Guide Line.

Joint Line Gap Pair - A joint line pair of precancelled coil stamps that shows the gap between the auxiliary plates used to print the precancel.

*Joint Line Pair - a pair of coil stamps produced from the rotary press with a joint line between them.  A joint line pair will contain one stamp from each of two different plates.  See also Joint Line.

Junk Mail - nickname for advertising send by bulk rate mail.