What's the mazda 3 license plate bolt size?

The bolts that Mazda3 (or the axlea, as it's known in Japan) uses M6 bolts: That's a metric 6 millimetre, with a 1 millimetre thread pitch. You can pick these up at Your local Ace hardware, or if You're wary about shopping in a pandemic, which is still raging as I type this answer for You, You can snag off Amazon. There, look for part number MXLIC-SS, which is going to Prime Ave's Stainless Steel License Plate Screws for Mazda. The good thing about these is there'll last a lot longer without rusting, and they're completely compatible with the Mazda3 . They run about $6 normally.