Good morning, David~
The turnbuttons are about 1.5 X 3.5 inches. I use Locust when I can.'
One key to the dimensions is the size of any hole-saw you have. I saw through the floorboard with a hole saw (and then sabre saw). I make the turnbutton about 1/8-inchs smaller in both dimensions so the fit is not too snug. For example, with 1.5 inch hole saw I would make the turnbutton 1-3/8" wide.
Hope this helps!
SJS