This is a Yi action ND filter holder suited for the TBS Jello Guard filters.
It's designed to be printed from flexible filament. Put the filter in place by stretching the holder before mounting on the lens.
It's designed for the ND8 filter, which is abot 1.85mm thick. I don't know the thickness of other filters, so I'll upload other versions when I find out, but the design can be very easily adjusted on demand. Here's the link to the model in onshape: https://bit.ly/2MiyDmo