When it introduced the “51” in 1941, the George S. Parker Company knew it had a winner. The pen was stylish but not flashy, durable but not clunky, and reliable but not over engineered. Over the next 31 years, the pen proved itself immensely popular. Parker discontinued the “51” in 1972. Parker is believed to have sold between 20 and 50 million “51”s; the exact number is not known because the company apparently stopped counting after the first 12 million.
Compared to many fountain pens, both its contemporaries and more recent models, the “51”, with its monochrome plastics and its tiny nib that lies hooded within a shell, might be considered a Plain Jane. But the “51” was not designed to be an eye-catching display piece. It was designed to be an everyday, hardworking, trouble-free, reliable writer.
Good engineering discipline dictates that form should follow function, and Parker’s engineers and stylists apparently followed that dictum. They applied the best available technology in the most effective way possible to perform the very difficult task of writing under virtually any conceivable conditions, and the fact that so many Vacumatic-filling “51”s are still in use over 60 years since the last one was produced is a testament to their success.
Courtesy Richard Binder, www.richardspens.com

DISCLAIMER ~ Due to the nature of silver being a very soft material all pens advertised with Sterling Silver or Coin Silver caps may have slight marks unless otherwise advertised as Perfect Caps.  Also Sterling and Coin Silver caps were originally Rhodium Plated and unless advertised as Perfect Cap the rhodium plating is most likely partially or fully worn.  This does not affect the cap in any way.