From my understanding
The 2's are wavy. I'm not much of an expert with the 2's LoL! All I'm know is 2a is loose waves, 2b is tighter, 2"c" is much tighter. (not sure there is a 2c. LoL!)
3a is the biggest curl. Not sure how big but it's the biggest curl before it's just considered wavy.
3b is like broomstick sized curls.
3c is between giant sharpie and pen sized curls. Lots of 4a's are actually 3c's. Just in the smaller end of the spectrum.
4a is drinking straw and smaller curls. The curls are very defined, just small. 4a and 3c are sometimes very close in appearance. So it's kinda a matter if opinion at times. A pen sized 3c and a straw sized 4a look pretty much the same.
4b is fluffy with no curls or more of a wave pattern than a curl.
4c is much like 4b. Some say 4c doesn't exist, where as I've seen a chart that breaks every type down to "f"!! So...
But don't place too much value on this typing system. It's more for descriptive purposes. What matters most is things like texture (silky, fine, course, wiry) and porosity. And even when you have your number, texture, and porosity your hair is still unique. And some things that work for others may still not work for you.
Hair is a tricky tricky creature.
😜🍸Sent LIVE from my JPhone 4 using some CurlTalk app. 😜🍸