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No, it's not a normalized thread, it's STANAG! The thread on this filter is NOT made to fit in both GOST and STANAG threads, and it won't seal with a GOST thread more than any other STANAG filter. |
The FP-5 filter canister was developed for the MP-5, which replaced communist-era masks in Polish military service. The adoption of this NATO STANAG 4155 filter canister came within a few years of Poland's accession to the military alliance.
Normalization myth
It's commonly (and inaccurately) believed that the FP-5 filter canister thread pitch is designed in such a way as to accommodate both GOST and STANAG compliant inlets as a deliberate transitional measure[1][2].
This is a false assumption: the thread on these filters doesn't differ from any other STANAG filter.
Variants
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Different threads: FP-5 (STANAG) on the left, P-5 (GOST) on the right
The FP-5 filter canister has a variant with a GOST thread, called P-5. These GOST threaded filters are older, and most likely expired. However, it is incorrectly believed that a standard FP-5 can thread onto GOST masks due to the relatively tolerant threads of the SHM-62u.