1. This rail adapter is compatible with the full range of tactical FAST helmets, ACH helmets, and MICH helmets with OPS Core ARC rails on the side 2. Compatible with HD-19 series tactical headsets/EAR-MOR M31, M32, M30, M32H, and M32X. Simply put, the ARC rail adapter accessory is suitable for headsets with earmuffs in the shape of a raised battery compartment on tactical headsets and an inclined battery compartment on the earmuffs 3. This ARC helmet rail adapter can rotate 360°, and the ARC rail adapter accessory position on the headset can also rotate, and the bracket arm can be easily retracted and adjusted to a comfortable position 4. The bracket is installed with a spring and rotation design, and the bracket arm can swing up and down. When not in use, the headset can be rotated to the back of the helmet to give your ears a good rest and heat dissipation