Sensible things, helmets. They come in about a million shapes and sizes and have specific names, but they aren't well known so one shouldn't assume readers know them. But using the correct name for a helmet style could save you wordage and avoid info-dumping in a moment of action. A little strategic reader education could come in handy -- can you show your readers the helmet and give it a solid description before the big fight scene?
This is not an exhaustive list, of course. It's just to get your brain burbling.
Bascinet: the "beaky" one, which took the pointy front design (very sensible -- you want incoming hits to be shunted off the side of your head) to an extreme. These generally came into use in late-14th century Europe. These often have hinged visors too, so tech level could be an issue.
Barbute: these are one-piece helms with a T-shaped opening for your eyes and nose/mouth. They look something like ancient Greek helmets, but they are a 14th and 15th century design. No moving parts, though, so tech level is less of an issue.
Sallet: a nice, smooth, aerodynamic look. The slit is to see through. Mid-15th century Europe.
Don't let your characters go outside without their helmets. Yes, it gets in the way of their sexy Fabio haircuts and probably looks odd with that strategically torn shirt that's falling off their god-like pecs. But it will keep them alive so they can kiss the girl. No, kiss her later. We've got work to do.
My characters are butt-headed, hormonal teenage knights -- can you tell?