Dec 12, 2021 · In a third class compartment (6'2" or 25mm) you get 2mm, a 5 mm window, 2mm, a 7mm window, 2mm, another 5mm window and a final 2mm. Measure in from the sides and you end up with an even distribution of apertures even if your overall measurement is slightly out. Rule all that onto the plastikard and cut it out.