[Jojo Zerach]

I've heard about these before, as well as seen a reproduction, though they seem to follow the more defflective spangehelm design. Were they for mounted use?
(By flat helmet I mean the very simple open design that looks like a spangehelm with a flat top.)

[Craig Peters]

Are you referring to the early great helms, like these? http://www.myArmoury.com/view.html?features/pic_spot_ghelm05.jpg

The image should answer your question.