and time and effort as well as providing a less well refined overall fencing construction design an important rib set back configuration is also shown in fig3 here the rib set back 50 which is at least 0 010 inches and preferably is in the range of 0 010 to 0 050 inches further minimizes flashing exiting the mating area of the securement zone 22 and 34 during ultrasonic welding of the caps to the structural members preferably the set back distance is chosen to be greater than between 50 to 100 of the vertical height of the welding rib for polyvinyl chloride thermoplastic material this set back is usually 0 010 to 0 050 inches this is because the welding rib 40 is positioned immediately adjacent to the capping securement zone inner boundary line 38 while being positioned spatially distant from and set back from the capping securement zone outer boundary line 36 thus movement of the excess fluid thermoplastic material during ultrasonic welding toward the bore 14 will be enhanced this is also an important consideration in the overlapping or external cap side mounted configuration 58 shown in fig8 here again we see the rib set back space 50 between the welding rib 40 and the capping securement zone outer boundary line 36 on the other hand the welding rib 40 extends all the way to the capping securement inner boundary line 38 in this configuration since it is overlapping configuration the capping securement zone inner boundary line 38 is not immediately adjacent to the bore 14 of structural fence member 10 however the set back of the welding rib 40 and the angular relationship between the.