LEWMAR Hatch vent complete or Service Kit of Seals 

Complete vent is grey and is supplied with template, fixings and instructions

No sealant is required

Can also be fitted  to deck

Instructions say use either an 80 mm or 3 " hole saw

Overall size is 170 mm

Service kit has 4 small O rings to seal the screws, main closing O ring and bedding seal

Standard kit has bedding seal self adhesive ring 91 mm overall diameter

Small is 70 mm

I have many years experience of selling Lewmar products and have extensive knowledge for providing spares for winches, windlasses, hatches,  portlights,  steering and deck hardware