Viral Bacterial filters for 500 B series vacuum/drill. Click on the 500 B picture to see the 500 B instruction book, which will detail the proper installation of these filters. Reorder item number is ACC-VB. On this web site they are sold as a pair. The 500 B will require two. Typical life of the filters is from 6 months to one year. When these filters are replaced the ACC-BF filter should be replaced as well.