The Zeiss Lens Shade for Distagon T* 25mm f/2.8 & 28mm f/2.0 ZE/ZF/ZK Lenses is suitable for EF, K, and F mount versions of 25mm f/2.8 and 28mm f/2.0 lenses from Zeiss.
Lens shades are primarily designed to prevent unwanted stray light from entering the lens, by extending and shading the end of the lens. In addition, since the end of the lens is extended, you also get the added benefit of some extra protection from accidental impact.