A 7 is a tool of the cobblers trade, and might be kept in his tool bag or cupboard, but I dont reckon its a tool, all the same. A hammer and chisel are tools, but I dont think anvil and bellows are, for example. Youve got to work on something with a tool, surely that is the essential feature. It transmits your effort in some way to the object you are working on.If yousharpen a sickle with a stone, that stone is a tool. But if you sharpen a chisel on a stone sitting on a bench, I dont think the stone is a tool.