Hobby shop or use this conversion to get something close:
http://bobmay.astronomy.net/misc/drillchart.htm
I believe this conversion chart also tells you the size of Losi piston holes, if you ever care to know....
Its a .052" bit
It's a little larger then 3/64ths (.052" X 64 = 3.328 64ths)
a #56 hole is just under 3/64ths (.0465" X 64 = 2.976 64ths)