[suicideneil]

No worries, you can buy 6mm bore pinions, or you can just do like 99% of other guys did in your situation and grind the shaft down; all you need is padded vice and a metal file / dremel and some digital calipers. Stick the motor in a bag and poke the shaft through it to keep out the filings, then work back & forth along the shaft ( ahem.. ) and keep checking until your 5mm bore pinions fit snuggly. Either that, or sell your $70 motor for a large profit on a heli/ plane forum...