From Manufacturer
The JetMag Pro 67MAG Magnetic Front Cap from NiSi is designed specifically for their JetMag Pro line of magnetic filters. This cap magnetically locks to the front of your filter, protecting it from dust, scratches, and moisture during storage or transport. Similarly, it allows you to keep your magnetic adapter ring attached to the front of your lens, saving you the time of screwing it on once you're ready to shoot. Just quickly swap the magnetic cap with one of the filters and you're ready to shoot. Its aluminum construction is both lightweight and durable for easy and safe carrying.