For those of you who own a nice gas mask, but it simply uses hard-to-find 60mm filters, this is the nice inexpensive accessory you need to adapt your 60mm mask to be able to use 40mm NATO threaded filters, which are much easier to find. Made of durable polymer, these little accessories make a WORLD of difference.
NOTES: This is for 60mm masks. It's not the other way around. I know I already said that, but I know people will ask the question.