Nib: Medium 2668 steel
Esterbrook SJ "The classic Double Jewel" Bright Grey Lever-filled
The "J" pen, introduced in 1948, is the classic postwar Esterbrook.
The classic double jewel J. These came in three sizes J (full sized), LJ (slender), and SJ (demi) and in the classic six colors.
The earliest double jewel models simply have the "Esterbrook" imprint, whereas most with the Registered symbol (®). J's have double round black jewels with the name on the clip.
*The Osmiroid nibs that interchange with the Esterbrooks are the ones for the Osmiroid "65" fountain pen from the 1960s and 70s