The SteriPEN FitsAll Filter is a pre filter to remove particulates from water before purifying. It is recommended that particulates be removed prior to treating water with a SteriPEN UV purifier. The FitsAll Filter cup also serves as an adapter that allows the SteriPEN Journey or Classic to be used with wide mouth water bottles in the inverted position. The FitsAll Filter's unique design offers flexibility to filter water into bottles with a wide range of mouth sizes. Water can be poured through the FitsAll Filter or you can submerge the combined FitsAll Filter and bottle of choice. Prefilter to remove particulates from water. Uses durable 4 micron screen. Fits all bottle sizes. Fits into narrow mouth bottles such as commercial water bottles, soft drink bottles, canteens and SIGG bottles. Fits wide mouth bottles such as such as Klean Kanteen, Gatorade and Nalgene bottles. Adapts for wider mouth bottles,only the cup is necessary. Lightweight and flexible for packing. Size:3.5 in. x 95mm 3.7 in. x 72mm 2.8 in.. Weight: 2.3 oz.