Something thin to put between two pieces of 1/8" thick 1 1/2" wide aluminum flat bar that are bolted together. A bearing that will allow the two pieces of aluminum flat bar to be held firmly together but move (the only way possible) against the spacer between them with as little friction as possible.
Would that be nylon? Delrin? What is it called? At the moment, my best guess is "thrust bearing". Even though the only thrust pushing the pieces together is the bolt that holds them together. I'm looking at McMaster.
Is there something not officially labeled as such that works well for that purpose? I have some spray Teflon silicone lubricant from Lowe's.
It would be a linear thrust bearing as far as I can see. Without getting crazy expensive I'd use nylon or teflon. I know M-C has some nice thin teflon sheet that you could just cut out and lay in. If you have more than a small amount of force, most plastic will tend to squash down and extrude out. I think teflon will be better than nylon in that regard
I don't know the specific torque but it will be little, shearing pressure between the two aluminum flat bar pieces might be in the tens of pounds or maybe greater, as they pivot against each other.
I don't have a riveter. Anything that holds the two aluminum flat bar pieces together with a pivot point in the center will do. Some sort of clamp-on nuts might work, like a cotter key but maybe disposable and without having to drill tiny holes through the rod.
At the moment, I'm trying to deal with slipperiness (and later weatherproofing) of the bearing.
Look into some UHMW tape. UHMW is the same plastic used for ski bases, lining hopper cars, etc. The tape is sticky, and makes an excellent bearing for what you are doing. Once you get a roll of it, you will have a few many other uses for it.
Another possibility ( question?) is anodizing the parts, to make the surface hard enough to slide. Would that work?
Ther are also Ceramic spray coatings that can be applied to aluminum, and reduce friction. I used to get pistons ceramic coated for racing. Google it.
Thirdly, some words on riveting.. If you use a riveted joint, a heavy hit will bulge the rivet all the way through. Light hits will peen over the ends, leaving the center loose.
Bearings work best with hard-against-soft (this provides for embedding of grit into the soft side), so plastic washers are a suitable solution. Delrin and some polyacetal plastics are intended for long life as bearing material, should be available in washer form. Brass (a washer, or even just a disc cut from shim material) will also work, might be better if the aluminum surfaces are hard (anodized). Even stainless steel might be OK, if the aluminum is not anodized (the aluminum is the soft side, then).
The 'bolt' will rub the sides of the hole, and some loosening of a nut can occur, so various tricks are common in this kind of pivot. Easiest, is to fill the hole with a shoulder bolt, and glue the nut in place. Shoulder bolts are expensive, though. Second easiest is to fill the hole with a (slightly short) tube and use nut/bolt through the tube to keep the joint together. Washers (and maybe Belleville springs) are important, use them freely. One side of the bolt could take a lockwasher, the other then has to have slippage (like, use a brass washer/ steel washer/lockwasher/nut).
I'm a big fan of riveting, but good rivets are hard to find, like cheap shoulder bolts. It's probably easy to order thousands, but try to find one the right size when you need it...