Filling cover brass.

The lid can be locked on the filler neck with a padlock. The filling cover is normally delivered with a gasket. This secures that the filling cover is tight when the lid is mounted.

Brass DIN 17660 CuZn40Si, seawater resistant
Gasket: Unilion
Thread for hoseadapter DS41
Thread: Pipethread G DS/ISO 228/1.