The waterproof round hatch has a outside diameter of 9.85″ with a inner 7.88″ spacing. There are 16 predrilled holes positioned at regular intervals to ensure a secure and safe attachment. There is also a EVA foam gasket that is positioned between the kayak and the hatch to ensure a watertight fit. On the lid of the hatch is a T-Knob locking system that once locked in place with a easy clockwise turn secure the hatch and its contents. On the T-Knob there is a locked and unlocked imprint as a guideline to ensure safety. The Hatch also has a light nylon insert bag attached to a solid fitted ring for that extra equipment that you want to safeguard.