The GP-5 being worn with a NATO 40 mm filter

DISCLAIMER: This article is not meant as a guide to make Russian masks CBRN rated, but a simple procedure to use NATO filters on GOST mask for simple DIY jobs. This tecnique puts stress on the thread, so it's not recommended for long time periods and/or rare masks.


This is a short article on converting GP-5 gas masks to 40 mm NATO. This procedure works with any 40 mm mask. Skip the notion part if you just want to use your Russian mask with 40 mm filters.

Some notions you might want to know

A big part of the gas mask community thinks that the sealing of the gas mask comes from the thread. Even if it seems like it -in fact, NATO filters don't seal on russian mask- ,its a wrong notion, because the sealin

A GP-7v thread before and after adding the rubber ring

g of the filter to the gas mask comes from that small rubber ring at the bottom of every thread (italian masks being an exception which I won't touch in this post). The reason why NATO filters don't seal properly with GOST threads is that the filter doesn't arrive far enough to touch the rubber disc and close properly: what this procedure essent

A hose thread before and after adding the rubber ring

ially does is shortening the path by adding an additional rubber ring.

It is possible to buy spare rubber discs to pursue this method, but unregular or makeshift rings work fine as well, they just need to be flat and touch both the normal rubber seal and the filter.

What you need

  • Your gas mask (obviously) or a gas mas

    A GP-5 thread before and after adding the rubber ring

    k hose
  • The rubber disc in your russian filter (it comes with every sealed russian filter, it's in the cap, look at the pictures)
  • Two compasses (the drawing tool, not the orientation thing)
  • A knife or some scissors sharp enough to puncture and cut rubber



The procedure's being pursued

STAGE 1: Put your compasses' point in the exact middle of the rubber disc and draw a circle with a diameter 1 cm smaller than the one of the rubber disc, making sure there is about 0,5 cm of rubber outside your circle (for the GP-5 filter's rubber disc it should be 3,6 - 1 = 2,6 cm , but I recommend doing your own measurements to be sure).

STAGE 2: Cut the inside circle you drew in the last step, making sure you don't cut more rubber than you need. It's better to make the ring larger rather than thinner.

STAGE 3: Lay your newly made rubber seal inside your 40 mm thread like in the pictures, making sure it's well centred (rubber disc size may vary from filter to filter, most fit a bit loose) .

STAGE 4 (optional) :glue the rubber seal to the thread making sure it's well centred.


If you glued the seal to the

Two NATO filter screwed onto a GP-5 after the procedure has been done

thread, you can just use the mask normally, but if you didn't, you have to screw the filter with the gas mask in your hands with the thread looking upwards to make sure the seal it's well centred and that it doesn't drop off.

Question and answers

  • Does this really work? It seems to easy to be true: I have tried this procedure on many masks, and I've tested all of them, they work perfectly, for detail look into the info part. I think most collectors should try this for themselves and see the result (begone, FP-5 reign!).
  • The filter sticks out quite far, will it fall off?: No, but you have to make sure the filter was screwed on adequately. I tried slapping the filter while I was wearing the mask, and it didn't fall off.
  • Why had nobody thought of this before?: no idea. It's so simple and easy, I'm quite baffled by this.

JeromeZP (talk) 19:01, February 1, 2019 (UTC)

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