I made someone change their studs last week - which I haven't done for a while.
The player gave me a little bit of 'but I've played in these for the last five weeks, and no other ref minded'
I got the captain over to tell him, and the coach came as well, huffing and puffing and rolling his eyes about the fuss of it all .... and what size feet did he have.
Then, coach asked the player to lift his boot so he could actually have a look at the studs and
'bloody hell, no he's right, mate, I see what he means - you can't play in those!'
(They were exceeding narrow - about 2-3mm!)
Happily the studs were replaceable and he came over before the kick off to show me the same boots with a complete set of new studs.