Discs weighing how much must have a maximum thickness of 6cm?

The correct answer is based on the IPF rule that specifies the maximum thickness for certain weight disc categories. Discs that weigh 20kg must adhere to a maximum thickness of 6cm to ensure standardization across competitions. This thickness limit helps maintain uniformity in the loading and balance of the barbell during lifts, which is critical for maintaining fairness and safety across all competitors.

In the case of the other weights, 10kg and 15kg discs do not have the same thickness restriction, as they are generally thinner, typically around 4-5cm, allowing for easier handling and stacking. Similarly, while 25kg discs are relevant in competition, they typically follow their own standards, often falling outside the 6cm maximum thickness requirement. Understanding these specifications is essential for referees and lifters to ensure compliance with IPF regulations.