I remember one time I was putting in a 8" speaker with phillips screws and slipped and punctured the surround. I noticed no difference between the other one that was fine, after a few years I tried to find the hole and couldn't even find it. This was on a foam surround though rubber might be different. For my SDX-15 I used #10-32 and #10-24 because I ran out of the 32 TPI because I stripped them. I think the 24 TPI is better because the threads are stronger and won't strip as easy. I don't like using t-nuts but I don't think I have much choice, I wanted to be able to remove the drivers a bunch of times if I had to, without worrying about stripping the wood.