Heh, even a primary school kid can tell you it won’t fit (I’d digress from kindergarten kids who have learnt basic math, but they haven’t learnt how to solve word questions involving math until they turn 7).

Bought a 58mm tamp for my 57mm portafilter in the hopes that maybe their measurements are slightly off so it might fit. These are precision instruments, and I expected it to fit? 58mm – 57mm = 1mm, and I expected it to fit? Dumb boy, now you have to go back to the shop and exchange it.

Logic says one thing, so does experience and reasoning. Somehow, sometimes, we think we can win through with luck. Well, the 57mm portafilter fitting a 58mm tamp is not one of those things.