This is the 1474th most frequent Russian word.
миллиметров
"Millimeters" - a metric unit of length equal to one thousandth of a meter.
In this sentence, 'миллиметров' is used to specify a measurement (a unit of length).
Ширина ленты составляет 10 миллиметров.
The width of the tape is 10 millimeters.
Here, 'миллиметров' is part of a quantitative evaluation, expressing a shortfall in size.
Он отметил, что недостаёт несколько миллиметров до нужного размера.
He noted that a few millimeters are missing to reach the required size.
'Миллиметров' is used here to indicate the magnitude of a difference between two measurements.