The table tops are not completely flat.  The plastic tips of the legs have a post on them and they are just loosely pushed into threaded holes.  The legs attach by screwing threaded studs into threaded holes in the bottom corners of the table top then, nuts, flat washers, and lock washers hold the legs on.  Each pair of legs have four holes drilled that fit over four of the threaded studs.  Some of the holes are drilled deeper than others and are not completely perpendicular.  One of the holes had stripped threads.  I didn't want to go through the hassle of repackaging and exchanging so I used some JB Weld in a couple of the holes.  If I had known of the poor quality, I wouldn't have purchased these tables.  Like most things nowadays, they are poorly Made In China.