The SF FH556-216A works with all Legacy cans (pre-SOCOM models).

Enables attachment of FA556SA suppressor to any M4, M16/AR15, Diemaco SFW, HK416, and to other 5.56 mm (.223 cal.) semi-auto, bolt-action, and assault rifles with Mil-Spec muzzle threads. The end of this adapter has open prongs. This adapter functions alone as a high-performance flash hider when the suppressor is removed. Machined from heat-treated stainless steel, finished in a tough, corrosion-resistant coating. 

[NSN: 1005-01-565-2672] 

NOTE: SureFire muzzle brakes and flash hiders also serve as adapter mounts for our Fast-Attach® sound suppressors. If you do not plan to attach a SureFire sound suppressor to your firearm, we recommend choosing a shorter-length muzzle brake or flash hider. SureFire muzzle brakes and flash hiders that mate with our overlap suppressor models are longer in order to extend rearward over the barrel, a feature that is unnecessary unless mounting an overlap suppressor.