underwires

While driving along the interstate the other day I saw a delivery van for a company called "Ace Women's Underwires". Underwires. A whole company dedicated to the manufacture, sale and distribution of underwires. The accompanying graphic led me to believe that the sold strictly underwires, not underwire bras. Just the underwire part. It's just not something that I think much about. It never occurred to me that someone had to make those. But giving it further thought I am still perplexed. Is the manufacture of underwires so labor-intensive that it deserves it's own company? Why wouldn't bra manufacturers just cut their own? Is it that specialized? Even if you were to produce different types of underwire bras (say, metal and plastic) you wouldn't think that you'd need to order the part. Even factoring in the size differences, surely there's some sort of machine that could be adjusted to cut different sizes of underwire material.

It got me thinking about other, similar products. What else would be just as ridiculous? So my criteria is:
1. It has to be product-specific. For example, zippers would not be a good example because zippers have many varied uses.
2. It can't be used in a do-it-yourself capacity. I imagine there are a few people out there that make their own underwire bras, but not enough, probably, to warrant and entire industry. Candle wicks would be a good example of this - lots of people make candles so there's probably enough to warrant a candle wick company.
3. Although it might be product-specific (say, fish tank rocks), it can't be bought separately. You can't buy a bra and then pick out an underwire to go with it.
4. Similarly, it's not usually replaced. Microwave trays, for example. If yours broke, you might just buy the tray and not the whole microwave.
EDITED TO ADD:
5. That thing is the only thing that company makes. For example, clothes-pin springs would probably not qualify, because clothes-pin spring companies probably make springs of all varieties, wouldn't you think?

I came up with a few items that would fall under this criteria (underwires being one):
* Swiss Army Knife Forks
* Mr. Potato Head Lips
* trash bag draw strings
* eyeshadow applicator tips

Can you think of more?