There may be feather tubes at the temples. Chinstrap rings are identical to Imperial helmets, although earlier examples have studs outside the cheekpieces instead. Brass helmets may be entirely tinned or silvered. Far Left is a lovely Gallic H by Stallari, owned by Legio III Gallica. Right is Greg Fabic with the Coolus G he made from a spun brass bowl .
Some examples are silver with red enameled centers.
Earguards, whether brass or iron, should at least appear to be made in one piece, even if welded. Coolus-type crest knobs may be turned or cast, while Imperial crest holders are made of sheet brass. Brass hooks or rings for securing the crest are also present on most Imperial-style helmets. Anneal well and bend to fit, re-heating if necessary to avoid bad puckers. Then slit the tube open around the inside with a Dremel tool and fit it into place, and hammer carefully to flatten it.