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2011 rule changes - starter hole clarification 03 February 2011

Last year some teams pushed the boundaries of the regulations by introducing unusually-shaped engine starters, thus allowing them to have similarly-shaped starter holes in the diffuser (most commonly a slot), bringing aerodynamic benefit by making the diffuser more efficient. The FIA issued one clarification on this during the 2010 season (the drawing shows McLaren's starter hole pre- and post-clarification), and for 2011 the dimensions of the hole have been even more explicitly defined.

FIA Technical Regulation
3.12.7 - No bodywork which is visible from beneath the car and which lies between the rear wheel centre line and a point 350mm rearward of it may be more than 125mm above the reference plane. With the exception of the aperture described below, any intersection of the surfaces in this area with a lateral or longitudinal vertical plane should form one continuous line which is visible from beneath the car.
An aperture for the purpose of allowing access for the device referred to in Article 5.16 is permitted in this surface. However, no such aperture may have an area greater than 3500mm2 when projected onto the surface itself and no point on the aperture may be more than 100mm from any other point on the aperture.
Additionally, any bodywork in this area must produce uniform, solid, hard, continuous, rigid (no degree of freedom in relation to the body/chassis unit), impervious surfaces under all circumstances).