The Aquatica O-Ring Kit for Aquatica Aqua View Viewfinder contain a main housing O-ring, two ports/extensions O-rings and a container of O-ring Lubricant and are recommended for traveling and general maintenance. Manufactured to precision tolerances required to hold a pressure seal on your housing and made of elastomeric material, it provides the means by which a watertight seal is formed. The o-ring, resembling a thick rubber band, is designed to establish a watertight seal when going underwater. A pressure test or immersion without a camera inside is after changing any O-ring, failure to perform this test could result in serious damage to your camera and lens should the O-ring be improperly installed.