This instructable assumes you have some knowledge of Thule car rack equipment.
I recently purchased a used set of four Thule 400XT towers and two load bars for $30. The towers did not include the original bolts to tighten the towers to the car's roof, so I had to source some myself. Also, the plastic washers that reduce friction between the bolt and the metal washers were missing.
The parts I've described are all available for purchase on Thule's website, but if you are in a situation where you need to set up a rack fast and don't have the time to wait for stuff to arrive in the mail, this will work for you.
Step 1: New Bolts
1) By some new bolts. I won't say what size to get in case your system is different than mine, but they are metric. The best way to buy the bolts is to bring the tower with you to your favorite store that carries a selection of metric bolts (mine is Ace Hardware) and find some "Allen" or Hex key" type bolts in the 40mm to 50mm range.
Step 2: New Plastic Washers
2) To fab the plastic washers, I used some scrap plastic I had in my garage. It was a softer type plastic, very durable. I first drew a pattern of four squares on the plastic the size I wanted the washers to be. Next, I drilled holes in the middle of each square that the bolts could fit through. Next I cut the squares out of the plastic with a hacksaw. Finally, I beveled the backs of the washers so they would seat good in the metal washers that came with the rack.
Step 3: Attach Rack to Car
3) Attach the rack to your car. Be sure you have the correct fit kit and instructions! If you have a fit kit but no instructions, you can get some at www.thule.com. I strongly recommend following the instructions carefully, don't assume anything. Once you have the rack attached to your car, a quick tip to make it easier to install again if you take it off is to take a sharpie and make small marks where the clips grip under the door seals. These will be hidden when the door is closed.