Abstract: An open end wrench and a socket wrench are described which are selectively adjustable to rotate fasterners dimensioned pursuant to the English system or the metric system. Both wrenches compris first and second elements having parallel surfaces spaced apart to engage flats, of a given width, on a fastener. Parallel linkage means control relative moventment of the two elements between first and second positions. In the first position, the linkage is parallel to the flat engaging surfaces and the flat engaging surfaces thereof are spaced for rotation of a fastener having flats of the given width. In the second relative position of the elements, the linkage means is generally normal to the flat engaging surfaces and the flat engaging surfaces thereof are offset, with one surface of the first element being laterally spaced from one surface of the second element a predetermined lesser distance for rotation thereby of a fastener having flats of a width approximately said lesser distance.