The FIA has given the all-clear to Mercedes' Formula 1 wheel hub rim design, after Ferrari requested clarification.
Sources have revealed that Ferrari approached the FIA in regards to the rear wheel rim and hub design that its title rival had used in recent races.
Ferrari asked why Mercedes was able to run with a rim design that featured a collection of holes that appeared similar to a concept that Red Bull was banned from using at the 2012 Canadian Grand Prix.
Red Bull's outlawed rims forced the team to make modifications to its front wheel hubs, because holes that channelled air from the brake ducts to the outside of the wheel were ruled to be moveable aerodynamic devices.
Under the then-article 3.15 of the Formula 1 Technical Regulations, teams were told that "any specific part of the car influencing its aerodynamic performance" must be "rigidly secured to the entirely sprung part of the car" and must remain "immobile in relation to the sprung part of the car".
The rotation of the air in the hub was deemed to have been energising the airflow, which was illegal under the article.
While Ferrari has had to grapple with its main rival making big gains since the Belgian Grand Prix, there has been a great deal of interest on the new wheel hubs and rims that have helped Mercedes better manage tyre temperatures.
At the Belgian Grand Prix, new wheel rims were fitted to the Mercedes with extra ridges aimed to helping cool the rear tyres.
This change was subsequently followed up with suspension tweaks and a new rear wheel hub design (below) at the Singapore Grand Prix - which was a race where Mercedes pulled off a major surprise as it ended up the quickest car.
But Mercedes fuelled further intrigue when pictures revealed that the new Mercedes wheel rims had holes inside where the hub attaches to it, as can be seen in this photograph below.
The presence of the holes pointed back to the Red Bull banned concept from 2012 where air channels were rotating to help with airflow.
The current concept of blown axles - which was pioneered by Williams in 2013 - has always been based on the airflow channel being fixed, as can be seen below, so there could be no grey area about the holes rotating.
To clear up the matter, Ferrari elected to query it with the FIA in order to ascertain if it needed to pursue its own solution or whether Mercedes had pushed things too far.
The FIA then looked in detail at the Mercedes design and concept, which one source described as "interesting".
The investigation has concluded that Mercedes' design has different intentions to the 2012 Red Bull system and is compliant with the regulations.
Both Mercedes and Ferrari have been informed about the FIA's ruling on the matter.
The dispute over the wheel design comes is the latest twist in a long-running dispute between the teams this year over design developments, which have included Ferrari's double battery system and mirror designs on both cars.