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Overhauling Bottom Bracket - Are Parts and Tools Universal Size?
I am replacing the entire bottom bracket on my Dahon Tailwind folder. The spindle, bearings, bearing cages and bearing races are all worn and loose. But I live in Vietnam, where "bicycle mechanics" do everything with a hammer and a screwdriver, and just end up breaking it worse for a small fee. So I have to order my parts from the US and have relatives bring them when they visit. In other words, I only have one shot at this and have to get the order right the first time. Within the next week!
My main questions: Are all the specs on the parts and tools for lower brackets in the BicycleTutor tutorials universal? And if so, can I order them in one go, from one place, on the BicycleTutor site?

All BBs are not the same, but there are only a few common variations. From your question I assume you have a loose ball bearing type and not a sealed cartridge unit.
It is much easier to buy a new cartridge type than to find a replacement of the older style. And the good ones do tend to last longer, especially in wet conditions. You need to know the width of the bottom bracket shell (68mm and 70mm are the common sizes), the length of the spindle (not including the threads if it has threaded ends), and the threading (which I assume would be standard english on a Dahon).
The spindle may have a code stamped in it to tell you the size (something like "3S"). See here for more info:
You would also want a cartridge BB tool which in not very expensive.
The only thing I don't know is if Dahon has some unusual set up in the BB to allow for the folding. You may want to contact them before you order anything.
Good luck

Thank you. Yes, I appear to have the loose ball bearing type. When I unscrewed the race on the non-drive side, several ball bearings fell out. The spindle was worn erratically, the bearing cages were crushed, and the bearings themselves were worn into an oval shape.

When you say "new cartridge type" are you referring to some kind of single unit with race, bearings, and spindle in one thing that I can just buy and insert? If so, what specs do I need from the bike, inside diameter of the bottom bracket? The inside diameter of the bracket tube appears to be 45mm and the diameter of the race from the non-drive side appears to be 42mm. The spindle that came out says "PF 3A".

I've attached a picture of the bike, spindle, and bottom bracket.
Yes, in the "cartridge" type the spindle and bearing are in a sealed unit that threads into the frame. They are not serviceable, but tend to last longer. It is hard to find the older style that you have much anymore as cartridges have taken over. Good picture at the top of this:
You need a "square taper" type, which is the most common. You need a spindle length that is within a few millimeters of the one on the bike now (don't measure the threaded parts that stick off the end, just to the ends of the square tapered parts). You should measure the width of the BB shell on the frame. Finally need to know the thread type. I'd be shocked if it is anything other than standard english threading. But I don't know much about Dahon.
I'd check out the forums on the Dahon site. But if you're in a huge rush and can't wait, buy a BB made for a road bike with a similar length spindle and english threads. Very good chance it will work fine (again with all the normal caveats). Buy a mid price range one. The cheapest really are lower quality, but no reason for a $100 BB.
You'll also need a tool like this:

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