Many war surplus helmets were converted to fireman use. I have seen many of them up for sale. The dead give away is that the old holes are plugged with leather and resurfaced with shellac. You can also see 2 extra holes in the top where the spike base was fastened. The nickel plated "comb" found on the fire helmet conversion only uses 2 of the original holes on top and then they punch in another down the back. If memory serves, the comb is held on by 3 screw posts...2 in the top and one down the back. There are also much heavier, taller fireman helmets up for sale but these were manufactured specifgically for fire use. The brass visor trim on these is also wider. B