About Round Type 3５ (O-ring specifications)

This device helps users recognizing if the light inside a room is on from outside. The indicator lens can be easily attached to the door by pushing it into the hole (prior drilling needed). The thin ring on both ends is designed with a wider surface to hide the mark of the drilled hole on the door.
It is a φ35 O-ring specification.Uses an O-ring to make it difficult to loosen.