Stegmeier® FBGL-G-FLEX 8' Gray Flexible Plumb Strip 14 per Case. Plumb strips are PVC corner strips used to square the top edge of a fiberglass pool (one piece) in preparation for setting a cantilever form. Strips are installed using the self-tapping screws provided. Tighter radii may be formed by adding additional relief cuts making plumb strip adaptable to virtually any pool.