of the metal into the grooves 36 is illustrated in fig3 through 5 and fig1 the illustration in fig3 is a section taken along lines 3 3 of fig2 fig4 is a section taken along lines 4 4 of fig2 and fig5 is a section taken along lines 5 5 of fig2 as illustrated in fig3 the lip is wider than the lip in fig4 and 5 the lip 62 is widest at the midpoint of the lip at line 3 3 and becomes narrower as it extends to the corners this narrowing of the lips 62 causes metal to be plowed from the mid point 80 to the ends 82 of the groove 36 of the fastener 20 to better fill the groove see fig1 arrow c the angle of the lips with respect to vertical also facilitates the movement of the metal within the groove and plows metal from the center to the outer side of the groove see fig1 arrow d as illustrated the wider lip at section 3 3 leaves less room between the lip at 3 3 and the walls 38 and 42 of the fastener 20 because there is less room the panel metal at this location must be displaced elsewhere and the path of least resistance is to the wider areas.