Info: 1 Pre-Filter Assembly with 4 Micron Screen
SteriPEN Pre-Filter (SP-PF). When clear water is not available, use the Water Bottle Pre-Filter by SteriPEN to filter out particulates and debris. It fits on Nalgene® and wide-mouth water bottles, including SteriPEN's Classic, Journey, Adventurer or Traveler bottles. The unit has a dual O-ring seal protection to prevent the sediment from getting into the bottle. Dimensions: 67mm (2.6 inch) outer diameter at the bottom, 47mm (1.85") high.
Simply screw the base onto the top of the target bottle in lieu of its regular lid (ensuring the prefilter is positioned with its tip facing up), open the tip of the air vent, and gradually pour water into the base (there is a collection ring about an inch deep).