The FAMCO FB Round Vent Base – Flat Roof is used with a Globe Vent or any other round based roof vents without a flange. The Flat Base FB is used for flat roofs with no pitch or slope. This product features a large flange for easy installation and leak protection. No field trimming required. Weather proof construction. Crimped for secure fitting of ventilation units. Quality constructed in 28-24 gauge Galvanized steel. The FAMCO FB Round Vent Base – Flat Roof comes in a range of sizes: 4 inch, 6 inch, 8 inch, 10 inch, 12 inch, 14 inch, 16 inch, 18 inch, 20 inch, 22 inch, and 24 inch. The FAMCO FB Round Vent Base – Flat Roof is manufactured by FAMCO in the United States and comes with a 1-year warranty against product defects and workmanship. If you have any questions about this product, please refer to the FAQs above or feel free to contact us by phone or email.