flag leaning ... | Golf Monthly

circular in cross section

I have never seen a tapered flag stick - I have seen some with sections of different diameter but never with a taper. 17/3 tells us it can however be tapered.

There's no minimum diameter, and whilst logically there's a practical maximum I'm not sure if it's designated in the rules! A 4" diameter flagstick might be considered a huge advantage for chipping close, but offer extremely little to the sink it brigade!