I'm looking into buying a medieval style helmet to add to my collection of hats and the one that has me interested has a lot of reviews claiming it's too large to just slap on.
Was that common? I know modern helmets use some kind of leather strap system on the interior to hold things on, was that how it was done in the old times?
A Viking to Norman era helm has what's called a "spider" inside, a leather web that attaches to the helmet brim and spreads the load (and impact) on the wearer's head. This leather piece would be cut to fit.
We can see a similar structure in the modern hard hat. It's adjustable, but it's still a flexible support.
(nb: cut to fit with an arming cap or similar padding under)