In the photo above, the left two straps are the single layer version, and the right two straps are the "regular" two layer, traditional NATO version.
We've been getting a lot of questions about "single layer" NATO straps. The single layer version is simply a normal NATO strap with the second layer of nylon [under the watch head] removed. This makes the strap wear noticeably slimmer and closer to the wrist, which is especially nice for those of us with wrists under 7". Removing this layer does not remove the protection of keeping the watch attached if one spring bar fails. That safety net is provided by the top layer that passes through the spring bars, not this secondary layer that is removed.
It is easy to modify a normal NATO strap into a single layer version at home using scissors and a lighter. The instructions to do so are below.
This is an optional modification, but it can be a game-changer for some. Removing the second layer of a NATO strap will allow the watch to sit lower on your wrist. The end result is a less bulky strap that wears more slim; great for those with smaller wrists. This mod allows you to position the buckle and keepers anywhere on your wrist. Instead of being on the side of your wrist, you could position the hardware to sit underneath. This modification can not be undone or reversed.
Remove the strap from your watch, and undo the second layer from the strap by pulling the long end through the floating keeper.
Peel back the second layer as close as you can to the last seam. Using a sharp pair of scissors, snip off the second layer. Try to cut cleanly in one fell swoop: do not "saw" at the nylon. This will minimize fraying.
To seal the nylon and prevent future fraying, hold a lighter flame 1/2" away from the seam for 3-5 seconds, moving around slightly to evenly seal the nylon. Don't hold the lighter too close or for too long, as the flame could leave a carbon deposit on the strap. Once sealed, you can now reinstall the strap.