The German Outline #2 cap is a soft spray cap. If you press lighter you get a skinnier line and if you spray harder you get a fatter line. The cap produces a thin line and is good to use for outlines and details.
Thanks to James from Oink Art for the video using the German Outline #2 cap.
The German Outline #2 cap works on the following spray paint brands: Krylon, Montana Hardcore, Belton Molotow and Ironlak. According to the Oink's video, you can use it on Krylon cans to make flares. It leaks on Rustoleum brand paint so you should avoid using it.