Knights Armament KAC M4QD (NT4 556) Flash Suppressor with kit, 1/2"-28
Knights Armament flash hider and NT4 suppressor adapter
First, this is one of the best 5.56 flash hiders out there. Period.
Next, this is the flash hider used on multiple military weapons, like the Mk18 and M4, so if you are a serious clone builder, you need this flash hider.
Finally, while many KAC parts are hard to find, this item is available most of the time.
from Knights Manufacturing:
The KAC M4QD Flash Hider is an effective flash suppressor that also serves as a platform for attaching a Knight's Armament quick detach QDSS-NT4 sound suppressor. Comes complete with a 7-piece shim kit.
Thread Size: 1/2"x28
Suppressor Compatibility: KAC QDSS-NT4