This generic Hatch cover with rim included, has a Bayonet Thread and has a 20cm diameter opening
This is a complete Hatch and Rim – Suitable to replace hatches on many kayaks especially generic brands fitted to kayaks such as Finn, Spirit and others. It is a bayonet style and can’t cross-thread like other kinds of hatches and is generally easier to open than standard thread hatches which can jam. We recommend (even if it is not necessary) replacing the rim at the same time as the hatch cover (if convenient).
The maximum diameter item that can be put in the hatch is 20cm
The hole that is required in your kayak deck (to fit the rim) is 22cm diameter
You can use this to replace a standard thread hatch but will need to replace the Rim (Female) section.