Knights Armament (KAC)
This is a steel flash hider, made in America by a military contractor who builds some of the best small parts in the business. Patterned after the NT4, but with a longer body, this flash hider looks the part, with some small cosmetic changes. The flash hider is also longer than the Knights NT4, which will allow this flash hider to be pinned and welded to a Block1 or Block2 build with the KAC RAS or DD RIS-II M4 rails. The longer length, along with a crush washer and perhaps a small spacer will get you to 16" on a 14.5" barrel, to make your clone build not an SBR, and street legal. The KAC NT4 is too short to pin and weld, so this is a perfect option.
Charlie's has tested this mil spec NT4 clone flash hider for fit with the KAC QDSS-NT4 Suppressor, and it fits fine. There is a little more play back and forth in the barrel than the Knights NT4, but not much more.
Note: This is 100% made in the USA, and not an airsoft toy. It has the look of the NT4, but not all the refinements and feel. In Charlie's opinion, this is a good substitute if you cannot find the Knights product, and maybe you plan to keep this until the KAC NT4 is available.
One additional feature is its length. At 2", this will nicely pin with a 14.5" barrel: 14.5" + 2.0" = 16.5", less 1/2 inch of threading = 16" barrel. The KAC NT4 will not make it to 16", as it is 1/8" shorter. Some have advocated using a spacer, which is possible, but takes away from the security that the threads offer to hold the suppressor tight.