wats g40 and g60 mean

"The German name G-Lader comes from the shape of the supercharger (Lader), which looks like the letter G. The displacer's spirals are either 40 mm deep or, in the larger version, 59.50 mm deep, i.e. close to 60 mm. This is the reason we see the engine designations G40 and G60 in the names of Volkswagen models in which it was used"