Doulton W9220402 Slimline Sterasyl OBE Ceramic Filter He Doulton W9220402 cartridge is open on both ends (OBE) and fits in standard 10-Inch filter housings The Doulton W9220402 Hollow Core OBE Filter features a Sterasyl ceramic outer shell with no core The Doulton Slimline Sterasyl ceramic shell issilver impregnated ceramic