Instruction images unclear - you must look at the images for 2-steps ahead to get this right the first time. Front and back of the seat base are unclearly marked until you realize that there are 2 bolt holes in the back of the seat base to attach the back in addition to the side slots that go in the left and right side arms. The side arms must be just loosely attached for the back to slot into place, then hold pressure while tightening.