Vintage fountain pen collectors love to call this pen the Sheaffer Dolphin. Sheaffer had 3 models they called the 500, 800 & 1000. These were among the first cartridge filling pens that Sheaffer offered. Any additional information I can offer would be nothing but plagiarizing the excellent article at PenHero.com.
The interesting grip section and nib arrangement carries an unhallmarked 14k, fine nib.
The unique thing about this pen is that is unused and still has its factory chalk marks that say "Fine, $10.00". This is often an attractive feature for collectors. Therefore, I have not inked or polished the pen but left it as is.
An empty Sheaffer cartridge will be provided with the pen.
Length Capped - 136 mm (5.4”) Uncapped - 119 mm (4.7”) Posted - 143 mm (5.6”). Diameter Cap - 12.8 mm (0.51”) Barrel - 10.8 mm (0.43”)