f the primary resin section shown in FIGS. 2A and 2B; FIG. 3B is a side view of the primary resin section shown in FIG. 3A; FIG. 4A is a plan view illustrating another modified form of the primary resin section shown in FIGS. 2A and 2B; FIG. 4B is a side view of the primary resin section shown in FIG. 4A; FIG. 5A is a plan view illustrating another modified form of the primary resin section shown