For metric and imperial nuts and screws with widths across flats from 10 to 32 mm 38 up to 1 14 self locking from 17 mm no slipping on the workpiece zero backlash gripping of metric or imperial hexagonal headed screws no rounding of bolt heads reliable and tight gripping of rounded rusty or thick coated bolts and screws ideal for work on vehicle brake systems quick tightening of bolted connections using ratchet action