110mm Hatch Cover.
This is an externally sealed hatch cover.
The gasket (body) is fixed to the hull of the boat and the A.338 O ring is placed around the gasket, under the small lip. The hatch cover lid is then screwed tight onto the gasket and forms a seal with the O ring around the external diameter of the hatch.
This hatch cover requires O ring A.338 to be installed for complete water tightness.
The O ring is installed around the outside of the gasket part (body) which is fixed to the hull, the lid is then screwed tight and forms a seal around the outside.