From Yocan:

The Yocan UNI Magnetic Ring was made exactly for the UNI Box Mod. This magnetic ring allows the Yocan UNI can accommodate the majority of the 510-threaded cartridges found on the market today. It makes for a seamless experience for vaping on-the-go. These rings are small enough that they can easily get lost, so make sure you always have one handy so you will always have something to attach your cartridges to. The rings are made using high-quality materials so they won’t easily break but make sure not to overtighten the 510-threaded connection since it may get you into the problem of making the threaded connections getting loose altogether.