From the Technical Resources Department. Update to the SMACNA HVAC Duct Construction Standards, Metal and Flexible, Fourth Edition, Figure 2-18 Corner Closures - Flanges.

This technical resources bulletin updates the language for corner fastening requirements used in conjunction with the T-25a and T-25b flanged transverse joint assembly.
TRB #01-25 Figure 2-18 Corner Closures - FlangesNov 24, 2025 — Member Update