It's a charging handle - Breek Arms AR-15 Warhammer Mod2 Ambidextrous Charging Handle

There's not a lot to say about a charging handle. The skeletonized handles aren't reducing weight if that's the purpose but as far as aesthetics go, I personally like the look. This was my second Breek Arms Warhammer Mod2. I prefer the larger ambi handles and this is the best I've found at a lower price point. It was half the cost of the Timber Creek charging handle on another build.