If it's threaded, it's not a cassette, strictly speaking, but a freewheel.
There are three national variations of freewheel thread found on older bikes (early eighties or before, though there are a few later exceptions): British, French, and Italian. British (BSC) is the only one of the three still made. A BSC freewheel will fit an Italian hub. The other combinations are close, but incompatible.
There's a slim chance your Mavic hub might have a French thread, but most that found their way to British shores were BSC. Is there a date code on the bearing cover? A 1990s hub is pretty certain to be BSC. A 1980s model might be French, but the odds are that it's also BSC.
Calmes dans le demi-jour
Que les branches hautes font,
Pénétrons bien notre amour
De ce silence profond.