vocabularies

The standardized basket/portafilter diameter of a semi-automatic espresso machine, in millimetres — the discrete sizes the accessory market is built around (49, 51, 53, 54, 57, 58 mm; 58 mm is the commercial standard). A token category (the sizes are a fixed set, not a free numeral), recurring across machines (L11); growing (L13).

Answers the question: portafilter size.