Quarantine Coloring Book
The Belgian A.G.5 was a very similar to the Italian P.43, with twin cheek exhale valves. This example was made by L'Anti-gaz in 1936.
Similar masks in my collection: Italian P43
Filter stamps bottom view
"W. 35 P BREVETE"
"P.V. No 102"
"TYPE AGREE PAR LE GOUVERNEMENT"