No, really. What does it designate, since Shimano's own web is cryptic on this.

HT were the hollow crankarms, HTII was supposed to be hollow spindles and Hollowglide are the chainrings.

So any hollow spindle should be HTII, i.e. all 2-piece cranksets should be HTII as per:
https://bike.shimano.com/en-EU/techn...lowtech-2.html

But then in Shimano specs:
https://productinfo.shimano.com/#/spec/ROAD/Crankset

So 57xx is HTII, but 47xx is not? It's a 2 piece crankset ...