A nut or a bolt has flats and corners. The corners are more easily damaged and do not offer the optimum grip for a tool. In developing the Metrinch tool system Jozef Ruzicka had the aim to design sockets and spanners, which would not only have longer effective life, but would also ensure minimal damage to the fasteners on which they are used. The patented Metrinch Wall Drive profile drives only on the flats and not on the corners. The dimensions of Metrinch sockets and spanners have been precisely calculated, so that a single Metrinch tool will operate on both metric and inch series fasteners. For example, with a spanner 19 mm it is possible not only to tighten or undo a metric nut or bolt, but also the inch bolts 3/4" AF, 3/8" BSW and 7/16" BSF. Even when such bolts have become worn, damaged or completely rounded by abrasion. A further major advantage in terms of application is that the Metrinch Wall Drive profile can be used on open-end spanners as well as on sockets and ring-spanners. Metrinch open-end spanners always provide a 4-point grip instead of the 2-point grip characterizing the traditional profile.