Xiaoyi YI action filter mount

Update (June 2019): the plastic ND filters I bought are garbage. The image is all grey and there are ugly reflections from the sunlight. I recommend the TBS Jello Guard filters now. They're made of glass and work a hundred times better. Here's a modification of this holder suited for the TBS filters: https://www.thingiverse.com/thing:3663318

This is a Yi action filter holder.
It's designed to be printed from flexible filament and it takes 27x27mm square filters. Put the filter in place by st