These twist pens look very similar to Gatsby pens, the difference being that the whole tube twists to extend the cartridge, not just the cap. This makes Sierra pens very user friendly for new users. Sierra pens take Parker style refills
This striking Sierra pen is made with deer antler. $28
This Sierra pen is has a slide-on label covered with 10 coats of CA glue. This process produces a hard, durable finish. With my name on it, this pen is clearly not for sale, but is shown here as an example.
These Sierra pens are made with ash wood from the University of Dubuque campus. They take Parker style refills. $28