The black Kaweco steel spring is DLC coated. The "Diamond like Carbon" coating is extremely durable and can withstand the stresses of everyday use of a pen fountain pen. It comes with a welded-on iridium grain at the tip and a precisely measured spring slot.
Note: This spring fits all fountain pens of the following Kaweco series:
AL Sport, BRASS Sport, STEEL Sport, AC Sport, LILIPUT, SPECIAL, ELEGANCE, STUDENT and DIA2