It’s true that hard materials can easily crack when fittings are close to the edge. We recommend our Sexkant (Hexhead) concrete screws, which are used without plugs; they provide stress-free attachment and therefore avoid cracks in the foundation. The screws’ Hi-Lo threads cut precisely into the hard foundation and provide unbudgeable installation. Pre-drill the foundation and blow out the hole before installation. Use a washer beneath the head of the screw when tightening to prevent the head from pressing into the foundation.