I hope #8 is big enough. That is what Hobie used for the stock furling line and sheet cleats.
I was at the lake today and installed the check block and cam cleat. The #8 screws fit an existing threaded hole fine, except for length. I ran into a problem with the screws hitting the outer aka that plugs into the crossbars on the kayak. I had to use some SS washers to shim the front and for the rear I cut off about 1/4" of the screws. I had #8-32 2" screws, but really needed 1 3/4", unfortunately hardware stores I visited have 1 1/2" and 2". Luckily I had a hacksaw with me
I look forward to sailing it with the new furling line cleat in the rear.
Jim