New to the forum, looking forward to the discussions.
I have never seen this style of Prussian kokade before with the elongated hole. Is this anything specific? It is the normal size for maybe a model 1899 officers helmet..
I can't find my exact example to show it but it is for the m15 war time officer with the faux chinscales. Your this strange cockade goes thru the 2 prongs m91 sidepost and then the prongs split up beneath the helmet.