This Olympus o-ring is for the front lid of the PFL-01 underwater protective case. This underwater protective case is for the Olympus FL-20 flash. 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.
O-Ring care guide