Looks like a 28.6 band and a 31.8 band. Some Shimano and some Suntour.
Some bands will do both sizes. Most won't.
Same system used in downtube shifters.
Campy had the adjustable clamp for a short time.
Suntour had one that bolted into a hole drilled into the seat tube.
These days, shims are often used. Or braze-ons.