This is a refill for Traveler's Brass Ballpoint Pen. Refill has black ballpoint ink with an extra fine tip for precise writing.
FLAX art & design is a genuine Oakland institution. Opening their first store in 1938, they're now on their 3rd generation of family ownership and have recently relocated to a beautiful new Downtown location that could best be described as a "toy store for artists." 80 years in and they're still putting art and community front and center. You can visit them at their own site here, or find more of their products right here on Keep Oakland Alive.