The Sterasyl Ceramic Filter is a self-sterilizing filter that can be re-used over again to provide absolute micron filtration down to 0.9 microns The Doulton W9220406 cartridge is open on both ends (OBE) and fits in standard 10 and # 34, filter housings The Doulton W9220406 Imperial Hollow Core OBE Filter features a Sterasyl ceramic outer shell with no core