With respect to uniform hats in general (and a slight thread drift), the RN caps of the 60s (white plastic top) had a metal grommet inside to keep the top taut.
None of us wanted to bear any resemblance to the Chieffie, i/c "parade training" at BRNC, with a hat as flat as a mortar board.
However, should any hat appear to be battle damaged, the first instruction was "off caps" and the presence of said grommet was checked - 5 days ROB should it have been removed !
Answer - one could remove the grommet and shorten it by about an inch with a pair of wire cutters........
Result - hat now looked more respectable, the grommet check drew a blank, and we now bore less of a passing resemblance to the local milk man.
Even better, later on, when flying suits with epaulettes and caps were considered adequate uniform during the working day, stuffing it behind the aircraft seat gave it a definite "experienced ace" appearance !