I use a couple of small piece of rubber inner tube repair patch fore and aft of the screw holes, and the standard screws fit fine.
When I put the forend on with the patches in place, I noticed that it didn't sit "square" on the bbl (couldn't slide a dollar bill all the way through). A little bit of sandpaper fixed that.
I never bothered measuring, but groups from my 7mm WM tightened up quite a bit.