Closure for high torque installation on a container

A closure for a container that has an opening to the container interior where a product may be stored and that has a screw thread form, said closure comprising:

• (A) a screw thread form for engaging said container screw thread form to permit said closure to be screwed onto the container;
• and
• (B) a peripheral, grippable wall having a plurality of circumferentially spaced ribs wherein at least some of said ribs each have
• (1) a leading side that generally faces toward the screwing on direction of rotation;
• and
• (2) a trailing side that (a) generally faces toward the unscrewing direction of rotation, and (b) has a hook-like configuration defining a recess which is open toward the unscrewing direction of rotation, in which said hook-like configuration has a distal end that is radially outwardly of said recess and that defines a projection extending toward the unscrewing direction of rotation relative to said recess;
• said closure wall between two adjacent ribs at the roots of the ribs defining an inner convex circular arc surface lying on a circular locus having a radius R2, in which at least some of said ribs extend a radial distance A beyond said inner convex circular arc surface radius R2;
• said projection of said rib trailing side extending in the unscrewing direction a distance F beyond the maximum depth of said recess as measured in the screwing on direction;
• said distance F being in the range defined between about 20% of radial distance A and about 40% of radial distance A.