Olympus o-ring is for the front lid of the underwater housing PT-E01. The housing PT-E01 is for the Olympus Evolt E-300 digital Camera. The o-ring resembling a thick rubber band is designed to establish a watertight seal when going underwater. 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.