Bicycle Mechanics - Bottom Bracket Bearing Cartridge Size ? ? ?

Hi folks,
I'm so confused. Pardon me, I'm from the world of one piece feed-through cranks and just arrived into the world of removeable crank arms and bottom bracket bearing cartridges.

How does one know which size/type/country one has on his/her bike? I read Campagnolo, Shimano, FSA? etc.. How does one know the measurement? I read 107, 111, 115, 118mm etc. etc. etc.

I would like to get a new bearing cartridge but have no idea which one I should buy.

Thank you. I'm referring to an old Sun adult trike, don't know the age. I would like to know how to measure it.

There are four measurements that define cartridge type bottom brackets:

1. Threading. "English" is by far the most common. Remember the drive side cup is left-hand threaded. Italian is the second most common but no longer common.

2. Bottom bracket shell width. The most common is 68 mm and most English threaded bb's are that width. Italian road bikes (with Italian threading) are 70 mm and some mountain bikes are 73 mm with English threading

3. End-to-end spindle length. The numbers like 107, 111, etc. refer to that dimension.

4. Interface type. The former standard was the 2° square taper available in ISO (Campy) and JIS (nearly everyone else). Shimano's proprietary splined design is called Octalink and a competing public-domain design is called ISIS.

Wow, thanks. That tells me everything.