These are soft mount arm guards made for the ImpulseRC Apex frame. They are great for protecting your arm ends from cracking and splitting. They also double as a motor soft mount to dampen vibration. If you choose to not soft mount, you can install the arm guards upside down.
The arm guards are also available in a version that has no lip that wraps over the carbon fiber arm so that you can still use the stock injection molded arm skids.