Williams and Haas rolled out their cars this morning with a T-wing mounted on top of the engine cover.
The aerodynamic device appeared on the Mercedes and Ferrari cars at their presentations last week, its function probably having to do more with optimising airflow to the rear wing rather than offering any sort of additional downforce.
Teams not running the T-wing are still in the process of evaluating its efficiency, as McLaren's Peter Prodromou confirmed at last week's MCL32 launch.
Toro Rosso's James Key also believed his team would test the device sooner rather than later.
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