The phrase "outer diameter" refers to the measurement of the widest distance across the outer edge or surface of a circular object, like a pipe or a ring. Full definition
Although it will retain its 39 - meter outer diameter, phase one will leave a hole in the middle. (sciencemag.org)
It can hold rolls with a weight of up to 30 kilogramme, with a width of 228 mm (9»), a 76 mm (3») core and a maximum outer diameter of 330 mm (13»). (primeralabel.eu)
The Rally 330s features a 330 mm outer diameter with an inner diameter of 285 mm and weighs just 320g (approx.) (reverie.ltd.uk)