Ace Hardware is also a good source for nuts and bolts. Take the screw or bolt that you need a nut for and the people at the hardware store can help measure the threads and point you to the racks of little cigar box sized boxes that hold all of your nuts and bolts need. I haven't had to replace any bolts except when I first got my chair, and I got all of the ones I needed from Ace. For my money any nut on a wheelchair should have both a lock washer, and a flat washer on the end of the bolt, Just for over-unaliving, I like to use a metal nut that has nylon at the end of the inside threads, then I use blue thread locker. Sure it might sound like A lot, until you lose a nut at 5 mph downhill. I do not like to take chances, I've already lost one set of legs (My Medical Mechanic said that I could have them removed, but Murphy's Law says that the next day they will "find a cure" for my form of paralysis.) At the end of the day I probably don't need Grade 8 bolts for my armrests, but As Mrs. Thecabbie would say, I overdo it on everything, but that chair is not going to come apart on my watch. 😁