Portugal Model 964 helmet.
Model 964 = 1964, the year this model was first used.
The Portuguese denomination is Capacete M964 NATO.
This helmet is in a very good condition. This helmet looks a lot like the French model TTA51.
The M964 is actually based on this French helmet.
It has a steel shell and a liner like the USA M1 and the French TTA51.
See Model 964 helmet liner
This picture shows a nice stamp inside the helmet shell of the lot code.
LOTE = lot code FMP 1-11.
FMP = Fabrica Militar de Portugal.
I haven't found anything about Fabrica Militar de Portugal but at this site https://www.cascoscoleccion.com/portugal/porotan.html
I found information telling FMP is Fábrica de Braço de Prata.