Hello Leone,
Very cool photos. I posted a couple of pictures of the exact helmet, right down to the screw through the center of the wappen. Most of the screws on examples like this that I've seen seem to be machine screws of the type that would not normally be used by manufacturers of pickelhaubes. The screw on my example appears to be a very old machine screw with a fine thread. The only brass piece on my helmet is the wappen, with the front peak trim and spine left off and no holes in the helmet for their installation. The spike on mine is steel with the fake rivet impressions around the base. Same green paint as well. Thanks for posting this.
Semper Fi.
Bryan.