It is a HSAT ( Helmet Steel Airborne Troops ) paratrooper helmet made by Briggs Motor Bodies ( BMB) in 1942 - as they all were. Collectors tend to call them "fibre rim" para helmets on account of the band around the circumference. Search this forum for fibre rim threads.
Yours appears to be original except for the paint on the outside - which is probably post-war applied. The original paint can still be seen on the inside.
It is a desirable helmet, but the post war paint will half it's value IMO.
Comment