This is Tamiya TA07 D Parts Suspension Arms Medium.
The suspension arm design from the TA07/TRF418/419 come in two different materials; fiberglass reinforced plastic and carbon reinforced plastic. The fiberglass reinforced plastic found in the TA-07 is soft by nature while the carbon reinforced plastic found in the TRF418/419 is harder in nature. The TRF419X was the first kit to introduce a "medium" stiffness material and it is now available for the TA-07 and TRF418/419 suspension A-Arm design. They will help in low traction conditions, giving improved control once fitted onto a TA-07 chassis or TRF418/419 machine.