Plug for hole in transom

[DrownedDesertRat]

The lower hole in the transom (drain hole?) in my boat needs a plug. The problem is, I can't find one that fits. It's larger than 3/4 inch, smaller than an inch and threaded. I founda 7/8 inch livewell plug but I can't get it in because of the threads (that's how I tore up my thumb). Any suggestions on getting this hole taken care of? Should I drill the hole larger so the 1 inch plug fits or should I just remove a bit off of the threads so I can get the 7/8 inch plug in? It's a fiberglass boat so I'm not too sure if I want to make the hole larger.
[signature]