From ARRI…
The ARRI Master Anamorphic Flare Sets are highly versatile and economical accessories for the ARRI/ZEISS Master Anamorphic lens series.
Each of the seven Master Anamorphic focal lengths has its own specific flare set, comprising easily replaceable front and rear glass elements with a special lens coating that encourages flaring, ghosting and veiling glare.
For more: ARRI.