Most Esterbrook J series pens that are still around are the 'double jewel' version, introduced in 1948. The first pens, however, were single jewelled pens, often known as 'transitionals' because they filled a gap between the Esterbrook Visumasters, introduced in 1941 and the J series.
The early transitional pens, from 1944, had a squared off barrel end:
The top picture is the later double jewelled pen. The Transitional clip does not have the Esterbrook name:
Both pens are very nearly the same size but have a very slightly different profile, the transitional pen is less tapered.
