According to Wikipedia, "The beam is 125 centimetres (4 ft 1 in) from the ground, 500 centimetres (16 ft 5 in) long, and 10 centimetres (3.9 in) wide."
The answer should have allowed for the metric measurement (10 centimetres), and for the actual Imperial equivalent – 3.9 inches.
© Macclesfield Quiz League 2018