Some more details on that threaded adapter:
Threaded Front Sight Base for M-14 and M1A Rifles
This front sight base made by SEI is a drop-in replacement for the factory front sight base and flash hider assembly on all M-14 and M1A rifles. It attaches to the barrel in the same way as the standard front sight base and flash hider assembly, but instead of a flash hider, it is threaded at the front to accept a wide variety of muzzle attachments to include muzzle brakes and flash hiders of different makes and models. This gives you far greater flexibility in using the best muzzle attachment for your requirements. It is threaded with 5/8x24 threads which is the most common .308 cal./7.62mm thread pattern for muzzle brakes and flash hiders. This allows you to mount an extremely wide variety of muzzle brakes and flash suppressors from across the firearms industry to this fine rifle.
The front sight base is the correct height for standard mil-spec or national match M14 front sights on a full length barrel. If using this on a shorter barrel like Springfield Armory Scout Rifle with an 18" barrel, then a taller front sight will be needed like a SOCOM-16 front sight in order for your elevation to be correct. This part finally lets you put any compensator or flash hider that you really want on your M-14 or M1A!
This part is made by SEI using stressproof steel which is machined to exacting tolerances and then hardened for durability under extreme use. This was originally a cast part that was then machined at key points, but it has been redesigned Spring of 2010 and is now a billet machined part making it even stronger than before. It has a parkarized finish. Does not include castle nut.
Features
•Allows mounting of standard M14 and M1A front sights
•Allows various muzzle attachments such as muzzle brakes and flash hiders with 5/8x24 RH threads