This is the small mesh net used by many troops from 1943 onwards. Whilst similar to the British 1/4" nets used by the likes of the 90th Infantry Division and the 82nd Airborne Division, these are actually quite different.
In an effort to increase the supply of helmet nets to troops in the ETO, US army camouflage factories were tasked with the manufacture of these nets. They were made by cutting up larger vehicle camouflage nets to a size to fit the M1 helmet and were worn by simply placing over the steel shell and holding it in place with the liner. Ours our generously cut from original vehicle nets to fit your helmet; as a result, some may have small holes or not be totally square.
I have made each one slightly larger than the sample I cut for myself, and the original I patterned that after. Why? Without a string around the edge they're tricky to fit on your helmet. By no means impossible, but certainly harder than a conventional 1/4" or 1/2" net. The extra size helps a great deal. The helmet I used to try them out on is an original 1942 produced fixed bail, so these should fit any M1 shell you might happen to own (M1, M2, postwar M1, euro clones etc).
The easiest way I've found out to fit these is to lay them square out on the floor and place you helmet shell (sans liner) in the centre. Then fold the edge on the rear of the helmet over first and secure your chinstraps around the back of your helmet. This holds the net in place sufficiently tight enough to prevent it slipping out, yet allows you to adjust it as needs be. Then simply flip the remaining edges over the helmet rim and place your liner in the shell as normal, squashing it all together. If this is difficult, use a little masking or medical tape to hold it all in place before fitting the liner. These stretch quite a lot, so don't be afraid to give them a good tug to get the desired results.