The TWSBI Diamond Mini AL is a pocket sized fountain pen with a piston filling system, making it a great daily workhorse at a pocket friendly. The Diamond Mini AL features a modern, eye-catching design, with a transparent acrylic resin body that shows off the pen's inner workings. About one inch shorter than the Diamond 580, the Mini is conveniently pocket sized, with a cap that can be screwed onto the back end of the barrel when the pen is being used