This is an Ikelite o-ring for Ikelite to Ikelite TTL Sync cord. This also ensures that there would be no leak on the sync cord. It is also compatible with SPD battery pack cable, and Pro Video Lite II cord.
This Sea & Sea replacement o-ring set is for the Sea & Sea 5 pin Nikonos sync cord. 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.