Beams and rafters were made by hand from tree trunks around 100 years ago. At that time this was not done by a machine, but only with diligence and perseverance.
Bars are available in thicknesses from approx. 10x12cm to approx. 24x26cm and in lengths from 0.5 to 13m. In addition, they have a rectangular cross-section and are not square - e.g. 14x16cm.
The indication of the beam dimension therefore always shows a certain fluctuation. See the description in your offer.