The filter thread size of HD PENTAX-DA 55-300mm F4.5-6.3 ED PLM WR RE is 58mm.
Below are links to the filters that we recommend you to consider for your PENTAX 55-300mm F4.5-6.3 ED WR:
Read our detailed HD PENTAX-DA 55-300mm F4.5-6.3 ED PLM WR RE Review