This Olympus o-ring is for all lens ports for the underwater housing PT-E01 housing. The PT-E01 housing 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.