Hi again James,
I haven’t measured my chisels but I suspect they are actually metric equivalents of standard Imperial sizes. Having said that, I don’t think I ever ran into a situation where the exact width in a chisel was a requirement. Even in the case of mortise and tenon work the marking gauges are normally set to whatever chisel width was convenient and appropriate to the task at hand. Even at that, a set of six decent chisels for less than nine bucks (with the 20% coupon and local sales tax) isn’t a bad deal.