Replaced both filters with Dyson 17, pre-filter and post-filter. The new filters I bought from Revain fit perfectly. I didn't even know my Dyson 17 had 2 filters. I've always serviced the pre-filter by flushing it, but I had no idea the post-filter even existed. There were no installation instructions with the filters when they arrived, but I did find installation instructions on YouTube. There are many Dyson 17 maintenance videos on YouTube. To keep your vacuum cleaner in top condition, be sure to watch some of these videos. I recommend changing the filter regularly.