I guess it depends on wich part of the shaft people refer to.
I gained 1 inch in base girth/upper base girth in a few months(2-3) by mostly concentrating on length gains with manual stretching and jelqing/uli/horse440/supra slammers/basically manual jelqing for expansion and hanging weights with a homemade Wench. I have measured pictures of 7” base girth since 2018, I was getting expansion like that when releasing weights from the hanger and letting the hanger a few more minutes on while getting slightly engorged post hanging set. I started pumping and then clamping 1 year after that, I don’t think I gained as much in permanent girth as I did in expansion girth, but it all seems to boil down to how much I work on it and keep the expansion going “forward”, resting, then doing it again and going for more expansion. I can now pump/clamp and measure 7+ mid-shaft girth, 8+ base girth, I know I even measured 9” base girth after long periods of pumping and short sets of 1 click cable clamp (3-5min) sets done right after. But mseg is probably only around 15cm still, but I quickly go over that if I want now. My smallest measurements now is 14,5 and usually a little more than that after 1-2 months of no PE whatsoever. I was 12,5 mseg when I started, 13,5cm base girth(2018 measurements after a few weeks of PE had already been done). Upper-shaft and glans gains seem to come easier now after 3 years already into it, I guess it’s probably from all the kegels I done, performing stronger and stronger kegels eventually. Glans expansion really seems to require high EQ, but it also seems to work with hanging and rings as well. I now measure 12,5 on a bad day right below the glans, usually it’s 13+, close to 13,5 and I can easily go over 14 cm upper shaft expanded girth now, I could never see that before, couldn’t even imagine it. It takes time, but things can be sped up with intensity. Insintex/prelude99 is now pumping with 10”x5” tubes, reaching the end of them.