Get the datasheet, look at the recommended PCB layout part of the datasheet, not the data on the component itself, and it says 0.7mm hole. So that's what you'd use, right?
But then again if it's an 0.5mm x 0.5mm square pin, then that's 0.7071mm across the hypotenuse, and you might want a little bit more room for error, so maybe 0.75mm (not standard?) or 0.8mm.