I've been thinking about putting together a thread sizing set, made up of nuts and bolts of numerous thread sizes, so you can identify a nut or bolt that you need to replace.
I went looking for one on google, and was really surprised that I couldn't find one. I've seen wall mounted sets at Lowes and Home depot, but they never have all of the thread pitches or uncommon sizes. I would do every size from #4 to 1/2", coarse, fine and super fine (if applicable) pitches, on this chart:
http://www.physics.ncsu.edu/pearl/Tap_Drill_Chart.html
Plus the same for metric. Probably 2 nuts and 2 bolts/screws of each thread.
Thats about 28 sizes in SAE. Lets say its the same for metric, 56 sizes total. 2 nuts and 2 bolts of each thread makes 224 total pieces. I have a really, really, really, really good source for hardware from an industrial hardware supplier near my parents house, and I feel like I could put together a kit, with labels and some sort of divided container, for less than $50, maybe even cheaper.
For me, thats totally worth $50, but I would probably have to buy enough hardware to make a handful of kits from the supplier (they hand-pick everything from stock, I can imagine them being super pissed if I went in and asked for 1 kit worth). Would other people be interested in something like this?