The skid block (plank)

Running the car lower than the post-Imola aerodynamic cuts intended, since ride height was policed only indirectly.

Nothing measured how low the car actually ran.

Ground clearance is downforce.

A 10 mm impregnated-wood plank with a maximum 1 mm wear, introduced from the 1994 German GP. Schumacher was disqualified at Spa for excessive wear.

Still in force and still producing disqualifications — Hamilton from the 2025 Chinese GP, and both McLarens from the 2025 Las Vegas GP.

The longest-lived rule in Formula 1, and the one that most reliably produces a modern disqualification. Introduced 1994, tightened in 2022, 2023 and 2025, still catching cars thirty-one years later.