The Prometheus Black Hop Up Bucking is basically the softer Prometheus Purple but designed to answer the call for a pre-denub'd bucking. This means that you can skip a step while flat hopping or r-hopping your gun by not having to worry about taking the nub and barrel alignment ridge. This bucking keeps the same well established quality and consistency of the Prometheus Purple and just simplifies your life. It does not include any nub and basically requires you to have a flat hop or r-hop due to the lack of a mound on the inside.
Prometheus is one of the top upgrade companies known for their high end barrels and hop up upgrades. Based out of Japan they've been releasing airsoft upgrade parts for over a decade and are a tried and true name.