The filter thread size of Panasonic Leica DG Vario-Elmar 100-400mm F4.0-6.3 ASPH Power OIS is 72mm.
Below are links to the filters that we recommend you to consider for your Panasonic 100-400mm F4.0-6.3:
Read our detailed Panasonic Leica DG Vario-Elmar 100-400mm F4.0-6.3 ASPH Power OIS Review