For a 2"x 1" batten which from the sheds will be 44mm x 19mm you will need 19mm + the length of the plug, around 32mm, so 50mm or 2". Follow KIAB's chart and in imperial you need a 8ga or a 10ga or in metric a 4mm or a 5mm with a red or brown plug. Personally I would use a 8ga/4mm screw with a red plug which requires a 6mm masonry drill. This is just my opinion. In this game you have to learn to convert between imperial and metric but it's a lot easier than plumbing sizes.