The review by Lock N Load stated that he would like to figure out how to interpret the numbers stamped on the side of the filter.
I found a manual for the Yugo/Serbian masks and filters with a English translation. Here is what it says:
Tags on the filter canister
On the casing of the filter canister in black is the year of manufacture (last two digits) and serial number.
82 – Manufactured in 1982.
003 - Number of series
Keepshooting.com has the best price for these filters if you can even find them in stock anywhere else.
make sure you get an adapter!
These are non-standard sizes, so make sure if you have a NATO (40MM) Mas that you get a hose adapter or something.
These are fine if you have JNA masks or something :)
Nice having 60mm filters available.
I love the fit and finish of my Finnish gas mask, and have one of keepshooting's 60mm/40mm adapters...but...it is nice having these available, at a really good price.
Lock N Load
Serbian 60mm Gas Mask Filter
Since 60mm threaded filters are relatively few in number and hard to find, it was great to find them here at KeepShooting.com
I'm sure that these filters have expiration dates, but have not figured out how to interpret the numbers stamped on the side.
The 40mm filters are very common and you can buy an adapter, but it was nice to have some 60mm filters that will fit the Serbian masks without the hassle of an adapter.