Need to know the wrench size for 10.9 screw My pedal just unscrew. It has a hexagon-headed screw with '10.9' screw label. Anybody knows what size of wrench I need for this screw?
10.9 is the type of steel alloy used, not the size of the hex key (aka allen key) you need.

Get a set of hex keys (almost surely a metric set is needed, given that its on a bicycle) and then try them out to see which one fits. I'd guess its something in a 3mm, 4mm, 5mm or 6mm range.