Step 5: Assemble
Refer to the photos and the PDF.
Place lengths of all-thread through the top and bottom holes on two pairs of 1x4s.
Place a washer and a nut on each end of each length of all-thread. Note: washers have a "belly" formed when they are punched out of the sheet of metal. Like a biscuit or cookie, the top edge is slightly rounded, and the bottom edge is a bit rough. Pay attention to the belly, placing the rough edge against the wood, and the smooth edge out. Pro.
Place the top and bottom shelves into position on top of the all thread, leaving 2" extending out past the uprights. The uprights clamp or pinch the shelves in place, so gently snug the nuts down to keep it all together.
Assemble the other pairs of uprights in place around the top and bottom shelves, leaving 26" between the uprights.
Fill all of the remaining holes with all-thread and loosely attach the nuts and washers.
Thread the remaining two shelves down the length of the unit, on top of the all-thread, and "snap" them into place.
A scrap block and a hammer may be necessary to "snap them" down.
Check the shelf assembly for square by measuring it for corner to corner. If the two measurements are the same, it is square.
Tighten all of the nuts, using, simultaneously, your tool of choice on each end of each rod. Just snug them up; it is not necessary to get them "gorilla" tight.
Tightening the nuts clamps the uprights against the shelves, holding them in place and providing shear strength (through friction) for the whole assembly. I know of an 8' tall, 12' long version of these shelves that has survived a few minor earthquakes while fully loaded with hundreds of books. Once the nuts are tightened on my smaller versions, I (all 240lbs of me) have a very hard time "racking" the shelves by pushing on one end of them in an attempt to get them to collapse: I can't.