Apparatus having controlled friction connection between two parts

Apparatus comprising a pair of parts, one of which has a continuous even surface that is engaged under a force against an opposing continuous even surface on the other part to frictionally inhibit relative motion in at least one direction between said parts, said apparatus being characterized by:

• A. said one part
• (1) having at its said surface, when in a nonengaged condition,
• (a) a plurality of strip-like hard zones which do not protrude from said even surface, have their lengths substantially transverse to said direction and which are laterally spaced apart and
• (b) strip-like soft zones between said hard zones which do not protrude from said even surface, and
• (2) having substantially greater hardness in said hard zones than in said soft zones;
• and
• B. the material of the other of said parts at said opposing surface thereof being of such hardness that when in an engaged condition under said force the differences in hardness as between said hard zones and said soft zones tend to produce in said opposing surface undulations in said direction.