I need the name of a part.

Aug 7, 2010
90
Catalina 22 Stockton Lake, Missouri
Sitting here feeling pretty stupid. I need to cut about a 4 inch hole in the side of the seats of my Daysailer to replace the wood that holds the centerboard tower braces to the seat.....and for the life of me I cannot think of the name of the thing used to cover the hole. Evidently I 'm so stupid I can't find one on a web site either. Any help appreciated....if you don't mind helping stupid.