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There is a bit of differences between the two, the PDE-1 features a five-point rubber head harness, with just one strap on the top. As seen on the CM-4 (or Bulgarian PG-1) mask(s). The rubber straps are also numbered, similar to that on the straps for the PMK-1 series of masks. It's key difference is a peripheral seal, (however this may have been added to models of later production, possibly ones made in the 80s to 90s.) it's also worth noting that this is the only M17 derivative that ever featured a peripheral seal.
However, it seems that the PDE-1 never had an updated variant that featured a drinking tube. It's possible that one has been thought of, but wouldn't work properly. The mask itself is made of a black rubber, possibly latex or butyl. Making it look similar in appearance to the US M17, which the mask is based on. The mask features a dark blue voice diaphragm, and sometimes has the same dark blue or matte black frames for the eye lenses (this appears to vary on the masks). As mentioned above, this mask is nearly identical to the M10, meaning its filters and inlet valves are entirely interchangeable with one another. Which leads to speculation that the mask might have been made in collaboration between Czechoslovakia and Bulgaria.
The Kit Edit
The mask comes with a brown canvas haversack with green straps, which stores the mask itself, filters, anti-fog stick, and the outserts. The outserts are stored in a green elastic cover, almost similar to that of a Soviet filter sock. It's obviously there to protect the outserts from becoming scratched during storage or when a new pair was issued to a soldier. The frame for the outserts also have the same the aformentioned deep blue colour.