Some fancy friction-fit lens tube covers for ETC profile lenses (full size). For those of us who store these on shelves, this keeps dust out of the inside of the tubes. Change up the colors to match your inventory system if you like.
The "Extra Fancy" model is the result of using a multi-filament printer. Basically the lowest layers were printed in a different color. This same effect could be achieved with any of the lens caps.
The author marked this model as their own original creation.