Okay so my new to me pool (bought new house that has ig pool) has no cover over the main drain. So i am going to be installing an sdx retro cover. Now the part i need help with, id rather not have tl drill into the concrete to put plastic anchors to secure the trim ring part down. So my main drain sump is 5 3/8" diameter and the part that looks to me where i can put screws into is 5 1/8" diameter. My question is, can i screw into these parts though as there is no hole there at all. Pics in next post. You can see on the left and right side there is little bumped out spots. But i dont wanna screw thru into them if they are not solid and then have a leak.