Seriously solid chairs. There are 2 tricks to assembly

1.  Don’t tighten the leg bolts until AFTER you have the bottom I base installed or else you won’t get the base on. If your chair is wobbly, loosen the leg bolts, stabilize the chair, then retighten. 
2. To screw on the seat, find a table that is higher than the seat back, place the seat upside down on the table and the chair upside down on top. Make sure you press down on the chair as you tighten the screw to keep the seat in contact with the rest of the chair.