M8 : Thread size 8mm, spanner size 13mm, equivalent imperial sizes 5/16" thread, 1/2" spanner. M12 : Thread size 12mm, spanner size 19mm, equivalent imperial sizes 7/16" thread, 5/8" spanner. M10 : Thread size 10mm, spanner size 17mm, equivalent imperial sizes 3/8" thread, 9/16" spanner.
eBay