Yonex V-mass 320 Irons | Golf Monthly

Wouldn't be surprised if it doesn't mean too much and was just of way of Yonex keeping track of the model iterations.

Think I've seen 250, 260, 270, 300, 350, 400 etc.

Bit like TM and M2, M4, M6 etc.
And Mizuno (although their system often defied logic!)